Neck-wearable communication device with microphone array

ABSTRACT

A wearable electronic device includes a neck-wearable housing, generally U-shaped, with an electrical connector; two in-ear earphones; two cords, with one end connected to one of the earphones and the other end connected to the connector. The two cords are mechanically connected to the housing. Points of connection of the cords to the housing are close to each other and form a dorsal node, and the two cords are mechanically connected to each other in their portions between the in-ear earphones and the dorsal node to form a suboccipital node. A microphone is placed in the housing on a front (chest) side of the user. A microphone is placed in the dorsal and/or in the suboccipital node. The microphones are used for determination of correlated and non-correlated components of audio signals. The correlated components are treated as a noise signal and the non-correlated components are a target signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 15/052,240, filed on Feb. 24, 2016, which is a continuation ofU.S. patent application Ser. No. 13/902,903, filed on May 27, 2013,which claims priority to Russian Patent Application No. 2012158157,filed on Dec. 28, 2012, all of which are incorporated herein byreference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to telecommunication devices, and, moreparticularly, to a neck-wearable telecommunication device.

Description of the Related Art

Wearable telecommunication devices based on a necklace, collar,neckband, headband or other similar load-carrying structure are oftenused as an interface between a human being and a technical system, whichmay be a telecommunication system, a computer system, an entertainmentsystem, a medical system, a security system, etc.

Known stereo headsets in the form of a necklace, collar, neckband,either a neck half-loop or a neck loop type, have predominantly twotypes of connection between earphones and the neck part: headsets withtwo side nodes, in which earphone cords are connected with the neck partand do not have connections between themselves, and headsets with asingle node, in which earphone cords are connected to each other and tothe neck loop in a single node.

A conventional headset (see U.S. Pat. No. 7,416,099B2) includesearphones connected through cords to a supporting structure, whichaccommodates a signal transceiver, and is connected to a necklace (neckloop). The headset comprises long unsecured portions of cords connectingthe earphones to the neck loop, because the additional length is neededwhen the user rotates and moves the head relative to the torso. Theheadset has two nodes and the length of the movable portion of the cordsin the headset is more than 19 cm. The cords hang freely along theentire length thereof in the air over the user's body surface, so theyhave slack and might tangle and cling to surrounding objects. Inaddition, the headset is difficult to wear under clothing, both in theoperational and non-operational position, i.e., when the earphones aretaken off the ears.

A known earphone storage structure (U.S. Pat. No. 7,936,895B2) includesa necklace (similar to a neck loop), two fasteners formed in the twoends of the necklace, and stoppers. The size of the fasteners is smallerthan the size of the stoppers and the size of the earphones, thereforethe earphones may be pulled out when they are not used. The stoppersconnection form nodes, and this device relates to headsets with two sidenodes. The earphone storage structure has the same limitations as theprevious device: cords have slack, and the structure is difficult towear under clothing, and managing it through clothing is not convenient.

A lanyard for a portable electronic device (U.S. Pat. No. 7,650,007B2)includes two side connection nodes and allows adjusting the length ofearphone cords, but the lanyard does not eliminate sagging of cords inthe operational position.

In a necklace-type audio device (WO 2012015257A1), earphone cords form aneck loop when they are attached at their ends to a jack disposed on theuser's chest, and crossed through two rings disposed in the back of thenecklace (neck loop), the rings being adapted to adjust the length ofthe neck loop and earphone cords. In this device, the length of thecords connecting the earphone to the necklace (neck loop) is even longerthan in necklace-type headsets with two side nodes; this contributes toslacking the cords, and the way of adjusting the length of cords in theheadset eliminates a possibility of wearing the device under clothes.

A known modular personal audio device (WO 2005022872A1) and (US20070021073A1) includes a necklace having a winding device for headphonecords. These cords are connected to the rear part of the necklace andmay be coiled when the headphones are in the non-operational position.However when the cords are in the operational position, they are stillloose and so remain movable, and freely hang over the user's head duringrotation of the head. Hook-type holders are provided for securing theheadphones to the auricle. This makes wearing the device noticeable andinconvenient. The device does not have any controls means.

A known headset (US 20020043545A1) includes a headphone and amicrophone, the headset provided in the form of a wire loop bearing thedevice connected to the headset. This makes wearing the headsetnoticeable and inconvenient. The device does not have any controlsmeans.

A known headset (US 2002065115A1) which includes one or two headphonesand one or two microphones, the headset provided in the form of a wireloop bearing the device connected to the headset. The headphones areconnected to the device by separate cords. This makes wearing theheadset noticeable and inconvenient. The device does not have anycontrols means.

A known loop (US 20070080186A1) for retaining an electronic device, hascords are located inside the loop, and the user is able to change thepoint where the cord leaves the loop and to adjust the length of theloose part of the cord by moving a clip. However, this makes wearing theheadphones noticeable and inconvenient during rotation of the head.

A known wire loop (US 20070053523A1) for retaining an electronic device,wherein the user is able to adjust the length of the loose part of thecords by moving a clip. However, this makes wearing the headphonesnoticeable and inconvenient.

A known headset (US 2008143954A1), (US 20110051982A1) is in the form ofspectacles comprising headphones to be secured on the spectacle framewhen the headphones are in a non-operational position and connected byseparate cords to an electronic unit located on the user's occiput. Theheadset has a considerable weight and the electronic unit observablyextends from the user's head surface. This makes wearing the headsetnoticeable and inconvenient.

A known headset (US 2008283651A1) includes a loop for bearing theheadset on the user's neck, headphones and a device for retracting andcoiling the cord extending from the headset to an external electronicdevice which may be placed in a pocket or fastened to a belt, etc. Thismakes wearing the headphone noticeable and inconvenient. The device doesnot have any controls means.

A known modular personal audio device (US 2009318198A1) includesheadphones connected by separate cords to an electronic unit comprisinga power source and located on the user's neck's back side. The separatecords are disposed at the level of lower part of user's auricles, sothis makes wearing the device noticeable and inconvenient.

A known wire loop (WO 2003103255A1) for bearing an electronic device,wherein the user is able to adjust the length of the loose part of theheadphone cords by moving a clip, and magnets are used to retain theheadphones in the non-operational position. However when the userchanges length of the headphone cords, size of the neck loop changescorrespondingly, and the cords comprise loose parts. All this makeswearing the headphone noticeable and inconvenient.

A known audio player (WO 2009019517A2) aggregated with a rigid headband,wherein an electronic device and control means are disposed in a rearpart of the headband located on the back surface of the user's neck. Arigid configuration of the player makes its wearing noticeable andcontrol turns out to be inconvenient.

A known headset (WO 2010019634A2) includes an open rigid loop having amicrophone located at one end thereof and headphones connected to theloop by separate cords. A loose part of the cord makes wearing theheadphone noticeable and inconvenient. A rigid configuration of the loopis incompatible with certain types of clothes.

Therefore, the conventional devices, first, include excessively longunsecured portions of cords that connect the head part of a headsethaving a neck loop (in headsets with a single node the length of freelyhanging cords is about 19 cm, and in headsets with two side nodes it isabout 25 cm) and, second, unsecured portions of cords in theconventional devices do not fit to the body surface. The cord slackcannot be fully removed without restricting the freedom of movement ofthe user's head. Therefore, when the devices are used, the cords eitherslack, tangle and cling to surrounding objects, or restrict freedom ofthe user's movement.

Therefore, no device suitable for constant wearing has been designed upto now, which device would have a small total length of freely hangingcords snugly fitted to the body and creating no impediments to movementsof the head. Such a device shall provide improved user experience byfacilitating easy use, assuring secure fixation thereof on the user'sbody, and preventing failures caused by the cords clinging tosurrounding objects.

In general, the degree of slack of cords depends on the followingfactors:

-   -   the length of movable portion of cords between fixed points. In        all conventional neck headsets this is the length of the cord        between an earphone and the neck loop, so the shorter the        movable portion of the cord, the less the slack is;    -   cord tension;    -   degree of adherence of the cord to the body surface;    -   position of the cords; cords disposed on a plane do not slack as        opposed to cords hanging in the air or lying above natural        depressions on the surface of user's body.

It shall be noted that in the description of the invention herein, awearable device or a part thereof may be put on the neck of a user andmay look like an article of clothing, e.g., a scarf or a neckerchief,which can be put on and used in the form of an O-shaped neck loop or anU-shaped neck loop

In order to concisely indicate a component designed and arranged to beworn around the neck, the following terms may be used: neck loop, neckset, neck strip, neck tape, neckerchief, neck strap, neck band,neckwear, neck-wearable housing, neck sheath, and so on.

The inventor has found by experimentation that the components disposedon the user's neck, shoulders and chest, being both in the form of aclosed loop (such as an O-loop) and an open loop (or a half-loop, or aU-shape), equally allowed attaining the same technical result when theneck-worn part of components were properly located adjacent to thedorsal part of the user's neck. In this case, the dorsal andsuboccipital nodes of the device are located in optimized positionsaccording to the mathematical models described herein, which isessential for attaining advantageous effects of this invention.

But, from a usability point of view, the two types of neck loops maydiffer from each other. In particular, an O-shaped loop can hardly beput on and taken off without unfastening thereof. Moreover, this istechnically difficult for a typical women-targeted device due to thesmaller size of the device. Unfastening the device at the rear side, asit is usual for the most necklaces, is not convenient due to presence ofthe dorsal node disposed on the dorsal neck side, which is one featureof the invention.

The inventor would like to highlight a wearable device comprising anU-shaped neck-wearable housing as a separate option. This option allowseasy put-on and take-off of the device and provides compact designthereof.

A wide range of wearable electronic devices appeared recently owing todevelopment progress in radio engineering and computer engineering.However, the problem of noise reduction in speech signals became evenmore pressing as the wearable devices may be used in a very noisyenvironment.

The easiest way of noise reduction in a speech signal is placing a lowsensitive microphone in a close vicinity of a user's mouth. But thiscauses certain usability problems as the microphone is clearly visibleand a support structure has to be used in order to fix the microphone inan appropriate position.

Another way of noise reduction in a speech signal is using a dual-portmicrophone which may be positioned somewhat more distantly from theuser's mouth, e.g., on the user's chest. A dual-port microphonefacilitates noise cancellation owing to processing two speech signalstaken from different directions. However, in order to assure effectivenoise cancellation by phase and volume processing, the distance betweenthe user's mouth and the microphone ports has to be exactly known, whichis impossible when the user tilts and/or rotates his/her head.

Moreover, the user possibly will have to bend his/her head towards thechest in order to maintain acceptable quality of the speech signal in avery noisy environment. According to scientific research, see [1],methods of digital processing a speech signal obtained from a singlemicrophone yielded substantial distortion of the signal and unacceptableseparation of speech and noise.

Still another way of noise reduction in a speech signal is digitalprocessing multiple speech signals obtained from a number of microphonesaggregated into a microphone array of a certain type. Extraction of atarget signal from a signal/noise mixture may be performed using variousalgorithms based on different mathematical tools. According toscientific research, see [1], the optimal number of microphones in amicrophone array was found to be in the range of three to five, as theless number of microphones ceased effectiveness of processing and thegreater number of microphones did not contribute in considerably betterresults.

A noise-reducing directional microphone array is disclosed in WO2007106399. The array comprises at least two microphones generatingforward and backward cardioid signals from two omnidirectionalmicrophone signals. An adaptation factor is applied to the backwardcardioid signal, and the resulting adjusted backward cardioid signal issubtracted from the forward cardioid signal to generate a first-orderoutput audio signal corresponding to a beam pattern having no nulls ornegative values of the adaptation factor. After low-pass filtering,spatial noise suppression can be applied to the output audio signal.Microphone arrays having one or more additional microphones can bedesigned to generate second- or higher-order output audio signals.

A mobile telephone with multiple microphones is disclosed in US2006147063. The telephone is equipped with multiple microphones whichprovide improved performance during operation of the telephone in aspeaker-phone mode. These multiple microphones can be used to improvevoice activity detection, which in turn, can improve echo cancellation.In addition, these multiple microphones can be configured as an adaptivemicrophone array and used to reduce the effects of room reverberation,when a near-end user is speaking, and/or acoustic echo, when a far-enduser is speaking.

Eye glasses with a microphone array are known from US 2014278385. Thepublication discloses a method of reducing noise by forming a mainsignal and one or more reference signals at a beam-former based on atleast two received audio signals, detecting voice activity at a voiceactivity detector, where the voice activity detector receives the mainand reference signals and outputting a desired voice activity signal,adaptively canceling noise at an adaptive noise canceller, where theadaptive noise canceller receives the main, reference, and desired voiceactivity signals and outputs an adaptive noise cancellation signal, andreducing noise at a noise reducer receiving the desired voice activityand adaptive noise cancellation signals and outputting a desired speechsignal.

A device and method for direction dependent spatial noise reduction isdisclosed in WO 2011101045. The device includes a plurality ofmicrophones for measuring an acoustic input signal from an acousticsource. The microphones form at least one monaural pair and at least onebinaural pair. Directional signal processing circuitry is provided forobtaining, from the input signal, at least one monaural directionalsignal and at least one binaural directional signal. A target signallevel estimator estimates a target signal level by combining at leastone of the monaural directional signals and at least one of the binauraldirectional signals, which at least one monaural directional signal andat least one binaural directional signal mutually have a maximumresponse in a direction of the acoustic source. A noise signal levelestimator estimates a noise signal level by combining at least one ofthe monaural directional signals and at least one of the binauraldirectional signals, which at least one monaural directional signal andat least one binaural directional signal mutually have a minimumsensitivity in the direction of the acoustic source.

A noise-reducing directional microphone array is disclosed inWO2014062152. The directional microphone array comprises at least twomicrophones mounted on opposite sides of a device and generates forwardand backward base signals from two omnidirectional microphone signalsusing diffraction filters and equalization filters. Each diffractionfilter implements a transfer function representing the response of anaudio signal traveling from a corresponding microphone around the deviceto the other microphone. A scale factor is applied to, for example, thebackward base signal, and the resulting scaled backward base signal iscombined with (e.g., subtracted from) the forward base signal togenerate a first-order differential audio signal. After low-passfiltering, spatial noise suppression can be applied to the first-orderdifferential audio signal. Microphone arrays having one or moreadditional microphones can be designed to generate second- orhigher-order differential audio signals.

An adaptive noise canceling arrangement, a noise reduction system and atransceiver are disclosed in WO 9723068. The cross-coupled adaptivenoise canceling arrangement comprises an adaptive cross-talk filterwhich is split into a prefilter section and an adaptive filter section,the sections using different input signals. The prefilter sectionestimates the desired signal from the input signal of the noisecanceling arrangement, and the adaptive filter section has its inputcoupled to the output of the noise canceling arrangement, a delaysection being provided between the input and the output of the noisecanceling arrangement. The prefilter section and the adaptive filtersection are separate filters.

Microphone arrays with rear venting are disclosed in US 2009003640 andUS 2012207322. Such a microphone array includes at least two physicalmicrophones to receive acoustic signals. The physical microphones makeuse of a common rear vent (actual or virtual) that samples a commonpressure source. The microphone array includes a physical directionalmicrophone configuration and a virtual directional microphoneconfiguration. By making the input to the rear vents of the microphones(actual or virtual) as similar as possible, the real-world filter to bemodeled becomes much simpler to model using an adaptive filter.

An Audio signal processing device is disclosed in US 2015125011. Thedevice includes frequency conversion units configured to generate aplurality of input audio spectra by performing frequency conversions oninput audio signals input from a plurality of microphones provided in ahousing, a first input selection unit configured to select input audiospectra corresponding to a first combination direction from among theinput audio spectra based on an arrangement of the microphones for thehousing, and a first combining unit configured to generate a combinedaudio spectrum having directivity of the first combination direction bycalculating power spectra of the input audio spectra selected by thefirst input selection unit.

A directional hearing system is disclosed in WO 9740645. The system isconstructed in a form of a necklace including an array of two or moremicrophones mounted on a housing supported on the chest of a user by aconducting loop encircling the user's neck. Signal processingelectronics contained in the same housing receives and combines themicrophone signals in such a manner as to provide an amplified outputsignal which emphasizes sounds of interest arriving in a directionforward of the user. The microphone output signals are weighted andcombined to achieve desired spatial directivity responses. The weightingcoefficients are determined by an optimization process. By bandpassfiltering the weighted microphone signals with a set of filters coveringthe audio frequency range and summing the filtered signals, a receivingmicrophone array with a small aperture size is caused to have adirectivity pattern that is essentially uniform over frequency in two orthree dimensions.

A super directive microphone array is disclosed in WO 9746048. In thearray, analog filters are used to band-limit at least two secondarymicrophone elements which are spaced from a primary microphone elementby a distance respective of their band limited outputs. The band-limitedsecondary microphone signals are digitized by an analog-to-digitalconverter. A signal processor performs a super directive analysis of theprimary microphone signal and the combined secondary microphone signals.A plurality of microphones may be arranged in a ring. Their outputs aredigitized, split into frequency bands, and weighted sums are formed foreach of a plurality of directions. A steering control circuit evaluatesthe relative energy of each directional signal in each band and selectsa microphone direction for further processing and output.

A microphone array subset selection method for robust noise reduction isdisclosed in WO 2011103488. The method includes selecting a plurality offewer than all of the channels of a multichannel signal, based oninformation relating to the direction of arrival of at least onefrequency component of the multichannel signal.

A microphone system for teleconferencing system is disclosed in WO9510164. The system comprises at least two directional microphones,mixing circuitry, and control circuitry. The microphones are held eachdirected out from a center point. The mixing circuitry combines theelectrical signals from the microphones in varying proportions to form acomposite signal, the composite signal including contributions from atleast two of the microphones. The control circuitry analyzes theelectrical signals to determine an angular orientation of the acousticsignal relative to the central point, and substantially continuouslyadjusts the proportions in response to the determined orientation andprovides the adjusted proportions to the mixing circuitry. The values ofthe proportions are selected so that the composite signal simulates asignal that would be generated by a single directional microphonepivoted about the central point to direct its maximum response at theacoustic signal as the acoustic signal moves about the environment.

A directional microphone is disclosed in WO 0239783. The microphonecomprises a microphone array having a plurality of microphone elementsof which one element is a rear element and the other elements areforward elements. A processor is connected to the elements. Theprocessor can be a hardware processor for processing signals or it canbe a software controlled system for processing signals. The processordetermines the arrival of a wave at one of the forward elements andthereafter establishes a window of opportunity for receipt of the waveat the rear element.

The window of opportunity is set such that only waves emanating from aparticular direction will arrive in that time frame, thereby enablingacoustic waves from that direction to be processed by the microphone andother waves from different directions eliminated. The angle of arc ofthe microphone from which acoustic waves are received and processed canbe set by changing the size of the window of opportunity t3−t2. In thehardware implementation, the processor includes filters, zero cross-overdetectors, monostables and a flip-flop for setting a timing signal andtriggering the flip-flop to control the switch so that if a wave doesarrive at the element within the bandwidth of the filters, an audiosignal corresponding to the wave is transmitted from the element throughthe switch to an output.

A method of estimating weighting function of audio signals in a hearingaid is disclosed in US 2009202091. The method includes estimating aweighting function of received audio signals, the hearing aid is adaptedto be worn by a user; the method comprises the steps of: estimating adirectional signal by estimating a weighted sum of two or moremicrophone signals from two or more microphones, where a firstmicrophone of the two or more microphones is a front microphone, andwhere a second microphone of the two or more microphones is a rearmicrophone; estimating a direction-dependent time-frequency gain, andsynthesizing an output signal; wherein estimating thedirection-dependent time-frequency gain comprises: obtaining at leasttwo directional signals each containing a time-frequency representationof a target signal and a noise signal; and where a first of thedirectional signals is defined as a front aiming signal, and where asecond of the directional signals is defined as a rear aiming signal;using the time-frequency representation of the target signal and thenoise signal to estimate a time-frequency mask; and using the estimatedtime-frequency mask to estimate the direction-dependent time-frequencygain.

Systems and methods of detecting a user's voice activity using anaccelerometer are disclosed in WO 2014051969 and US 2014270231. Themethods start with a voice activity detector (VAD) generating a VADoutput based on (i) acoustic signals received from microphones includedin the mobile device and (ii) data output by an inertial sensor that isincluded in an earphone portion of the mobile device. The inertialsensor may detect vibration of the user's vocal chords modulated by theuser's vocal tract based on vibrations in bones and tissue of the user'shead. A noise suppressor may then receive the acoustic signals from themicrophones and the VAD output and suppress the noise included in theacoustic signals received from the microphones based on the VAD output.The method may also include steering one or more beamformers based onthe VAD output.

A three-dimensional sound compression and over-the-air-transmissionmethod during a call is disclosed in WO 2013176959. A wirelesscommunication device records a plurality of directional audio signals.The wireless communication device also generates a plurality of audiosignal packets based on the plurality of directional audio signals. Atleast one of the audio signal packets includes an averaged signal. Thewireless communication device further transmits the plurality of audiosignal packets.

A headset and a method for audio signal processing is disclosed inEP2884763. The headset comprises a first pair of microphones outputtinga first pair of microphone signals and a second pair of microphonesoutputting a second pair of microphone signals; a first near-fieldbeamformer and a second near-field beamformer each configured to receivea pair of microphone signals and adapt the spatial sensitivity of arespective pair of microphones as measured in a respective beamformedsignal output from a respective beamformer, wherein the spatialsensitivity is adapted to suppress noise relative to a desired signal; athird beamformer configured to dynamically combine the signals outputfrom the first beamformer and the second beamformer into a combinedsignal, wherein the signals are combined such that signal energy in thecombined signal is minimized while a desired signal is preserved; and anoise reduction unit configured to process the combined signal from thethird beamformer and output the combined signal such that noise isreduced.

A method for three-dimensional sound capturing and reproducing withmulti-microphones is disclosed in WO 2012061151. The method oforientation-sensitive recording control includes indicating, within aportable device and at a first time, that the portable device has afirst orientation relative to a gravitational axis and, based on theindication, selecting a first pair among at least three microphonechannels of the portable device. This method also includes indicating,within the portable device and at a second time that is different thanthe first time, that the portable device has a second orientationrelative to the gravitational axis that is different than the firstorientation and, based on the indication, selecting a second pair amongthe at least three microphone channels that is different than the firstpair. In this method, each of the at least three microphone channels isbased on a signal produced by a corresponding one of at least threemicrophones of the portable device.

A Bluetooth microphone array is disclosed in U.S. Pat. No. 8,295,771.Signal processing resources of a wireless telephone and multi-channeltransmission capabilities of the Bluetooth transmission are used tosuppress the background noise. The wireless telephone system includes aBluetooth transceiver communicating to a wireless telephone through amulti-channel Bluetooth transmission, and an array of microphonescoupled to the Bluetooth transceiver. The array of microphones includesa first microphone producing a first audio signal output and a secondmicrophone producing a second audio signal output. The first audiosignal output and second audio signal output are transmitted to thewireless telephone through the first channel and second channel ofmulti-channel Bluetooth transmission respectively. The system and methodof the invention allow using low cost Bluetooth transceiver(s) withmultiple microphone arrays to provide the background noise suppression.There are numerous other known devices and methods in the art. Thefollowing references are exemplary: WO 2012061151; CN 202998463; US2012020485; US 2015245129; US 2012087510; U.S. Pat. No. 6,594,370; US2011293103; US 2011317858; WO 2005094157; EP 2736272; US 2013101136; US2015049892; US 2010131269; U.S. Pat. No. 4,751,738; U.S. Pat. No.5,737,430; U.S. Pat. No. 5,563,951; U.S. Pat. No. 5,757,929; WO2004028203; U.S. Pat. No. 6,424,721; U.S. Pat. No. 9,202,455.

However, no relevant information has been found on defining an optimizedmicrophone layout in an array, based on peculiarities of the sound wavesgenerated by a speaking user and propagating in the area of the user'shead. Thus, the inventor performed extensive research works in order todefine an advantageous microphone layout in a microphone array, whichallowed him building an advanced model for implementing principlesdescribed in his earlier publication [9]. Further development of theseprinciples ensured the inventions set forth in the following descriptionand drawings.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a headset for a mobileelectronic device or by a wearable telecommunication device comprisingearphones that substantially obviates one or more of the disadvantagesof the related art. A headset for a mobile electronic device or awearable telecommunication device comprising earphones, which preventsubstantial changing the user's appearance while wearing thereof, andassure convenient use with no restricting freedom of user's movement,and can be effectively controlled directly through the user's clothes.

These and other advantages are assured by a headset for a mobileelectronic device, comprising: a neck-wearable housing having agenerally U-shape with an electrical connector attached thereto, twoin-ear earphones, two cords, each connected at one end to acorresponding in-ear earphone and connected at its other end to theelectrical connector wherein the two cords are mechanically connected tothe neck-wearable housing, and points of connection of the cords to theneck-wearable housing are in close proximity to each other and form adorsal cord connection node, and wherein the two cords are alsomechanically connected to each other in sections between the in-earearphones and the dorsal cord connection node to form a suboccipitalcord connection node at the connection point.

In the exemplary headset the dorsal cord connection node and thesuboccipital cord connection node may be located on a dorsal surface ofa neck, and cords in sections between the in-ear earphones and thesuboccipital node may be located over an auricle.

In the exemplary headset the suboccipital cord connection node may be aclip adapted to move along the two cords for adjusting a length of thetwo cords, the suboccipital node may comprise an electrical connectorfor disconnecting the cords.

In the exemplary headset the cords may be a helical spring in a sectionbetween the suboccipital and dorsal cord connection nodes.

The exemplary headset may further comprise an electronic unit, buttons,a power supply.

The exemplary headset may further comprise at least one noise reductionmicrophone array disposed on the mobile electronic device.

In the exemplary headset the neck-wearable housing may be flexible in atleast one location.

The above-stated and other advantages are also assured by a wearabletelecommunication device, comprising a neck-wearable housing with anelectronic unit attached thereto, two in-ear earphones, two cords, oneof which connects to one of the in-ear earphone to the electronic unit,and the other cord connects the other in-ear earphone to the electronicunit; and a microphone array for picking up and processing a user'svoice, the microphone array comprising a front microphone, a rearmicrophone and a processor, wherein the two cords are mechanicallyconnected to the neck-wearable housing, and points of connection of thetwo cords to the neck-wearable housing are close to each other and forma dorsal cord connection node, and are further mechanically connected toeach other in sections between the in-ear earphones and the dorsal cordconnection node to form a connection point wherein the suboccipital cordconnection node, the dorsal cord connection node, and an area of thehousing close to the dorsal cord connection node form a rear portion ofthe wearable telecommunication device wherein the rear microphone isfixed on the rear portion and wherein a front-facing portion of theneck-wearable housing is in contact with an upper chest when worn by theuser.

In the exemplary device the rear microphone may be is fixed on thesuboccipital cord connection node, on the neck-wearable housing close tothe dorsal cord connection node, between the suboccipital cordconnection node and the dorsal cord connection node, or on theadditional spring between the suboccipital cord connection node and thedorsal cord connection node.

In the exemplary device the rear microphone may detect surroundingnoise, and wherein a correlated portion of the signal from the rearmicrophone and the signal from the front microphone represent noise,while an uncorrelated portion of the signal represents a useful data.

In the exemplary device signals from the rear microphone and the frontmicrophone may be ignored when their correlation is above a pre-definedthreshold.

In the exemplary device the front microphone may be fixed on thefront-facing portion of the neck-wearable housing.

In the exemplary device the microphone array may include at least twofront microphones, wherein the two front microphone may be fixed on thefront-facing portion of neck-wearable housing at a substantially thesame height when worn by the user and one of the at least two frontmicrophones may be close to or below a right clavicle of the user, andthe other of the at least two front microphones may be close to or belowa left clavicle of the user.

The exemplary device may further comprise at least one gradientmicrophone array comprising at least two front microphones fixed on thefront-facing portion of the neck-wearable housing at different heightswhen worn by the user, wherein the gradient microphone array may be usedto determine a directional diagram of received sound waves.

The exemplary device may further comprise at least one phased microphonearray comprising at least two front microphones fixed on thefront-facing portion of the neck-wearable housing at different heightswhen worn by the user, wherein the phased microphone array may be usedto determine a directional diagram of received sound waves.

The exemplary device may further comprise an electronic accessory in aform of a wrist watch or a finger ring which may be wirelessly connectedto the electronic unit, wherein the electronic accessory may include thefront microphone.

The exemplary device may further comprise an electronic accessory in aform of eyeglasses, which is connected to the electronic unit, whereinthe electronic accessory may include the front microphone.

In the exemplary device a neck-wearable housing may be generallyU-shaped or O-shaped and the neck-wearable housing may be flexible in atleast one location.

The above-stated and other advantages are also assured by a wearabletelecommunication device, comprising a neck-wearable housing configuredto be mounted on a human body and in contact with back, left, rightsides of the neck and upper chest and having at least one electronicunit attached thereto, two in-ear earphones, two cords, one of whichconnects to one of the in-ear earphone to the electronic unit, and theother cord connects the other in-ear earphone to the electronic unit, amicrophone array for picking up and processing a user's voice,comprising a front microphone, a rear microphone and processor, whereinthe two cords are mechanically connected to the neck-wearable housingand points of connection of the two cords to the neck-wearable housingare close to each other and form a dorsal cord connection node, and arefurther mechanically connected to each other in sections between thein-ear earphones and the dorsal cord connection node to form asuboccipital cord connection node at the connection point, wherein therear microphone is on a portion of the neck-wearable housing configuredto be in contact with a back of the neck when worn by the user; andwherein a correlated portion of the signal from the rear microphone andthe signal from the front microphones represents noise, while anuncorrelated portion of the signal represents useful data.

In the exemplary device the rear microphone may be fixed on thesuboccipital cord connection node, the neck-wearable housing close tothe dorsal cord connection node, between the suboccipital cordconnection node and the dorsal cord connection node, on an additionalspring between the suboccipital cord connection node and the dorsal cordconnection node.

In the exemplary device the front microphone may be fixed on a portionof the neck-wearable housing that is in contact with the user's chestwhen worn by the user.

In the exemplary device signals from the rear microphone and the frontmicrophone may be ignored when their correlation is above a pre-definedthreshold.

The exemplary device may form an output signal e_(n) as:e_(n)=d_(n)−y_(n), where y_(n) is a correlated signal representingfiltered noise calculated as: y_(n)=w_(n) ^(T)x_(n), where x_(n) is acombined signal from the rear microphones, d_(n) is a combined signalfrom the front microphones, w_(n) are adaptive filter coefficientsdefined as: w_(n+1)=w_(n)|μe_(n)x_(n), where w_(n+1) is a set ofcoefficients at a current moment of time n+1, w_(n) is a set ofcoefficients at a previous moment of time, n is defined by a clock rateof the incoming data stream, μ is a positive value defining stabilityand convergence rate.

The exemplary device may form an output signal e_(n) based on aFiltered-X Least-Mean-Square (FXLMS) Algorithm: e_(n)=d_(n)−P(z)y_(n),where d_(n) is a combined signal from the front microphones, P(z) is atransfer function, and y_(n) is a correlation signal defined by:y_(n)=w_(n) ^(T)x_(n), where x_(n) is a combined signal from the rearmicrophones, w_(n) are adaptive filter coefficients defined as:w_(n+1)=w_(n)+μe_(n) r _(n), where w_(n+1) is a set of coefficients at acurrent moment of time n+1, w_(n) is a set of coefficients at a previousmoment of time n, n is defined by a clock rate of the incoming datastream, μ is a positive value defining stability and convergence rate, r_(n) is a vector formed by current and previous values of a filteredbase signal r_(n) according to: r_(n)={circumflex over (P)}(z)x_(n),where {circumflex over (P)}(z) is based on a Least Mean SquaresAlgorithm that corresponds to a finite impulse response (FIR) filter.

In the exemplary device the microphone array may include two frontmicrophones, wherein the two front microphones are fixed on a portion ofthe neck-wearable housing that is in contact with the user's chest andat a substantially the same height when worn by the user and one of thetwo front microphones is close to or below a right clavicle of the user,and the other of the two front microphones is close to or below a leftclavicle of the user.

The exemplary device may further comprise at least one gradientmicrophone array comprising at least two front microphones fixed on thefront-facing portion of the neck-wearable housing at different heightswhen worn by the user, wherein the gradient microphone array may be usedto determine a directional diagram of received sound waves.

The exemplary device may further comprise at least one phased microphonearray comprising at least two front microphones fixed on thefront-facing portion of the neck-wearable housing at different heightswhen worn by the user, wherein the phased microphone array may be usedto determine a directional diagram of received sound waves.

In the exemplary device the rear microphone may be used as a detector ofsurrounding noise wherein a correlated portion of the signal from therear microphone and the signal from the front microphone representsnoise, while an uncorrelated portion of the signal represents a usefuldata.

In the exemplary device signals from the rear microphone and the frontmicrophone may be not transmitted when their correlation is above apre-defined threshold.

In the exemplary device the neck-wearable housing generally may beU-shaped (or an otherwise open shape) or O-shaped (or an otherwiseclosed shape) and the neck-wearable housing may be flexible in at leastone location.

The above-stated and other advantages are also assured by a wearabletelecommunication device, comprising a flexible neck-worn sheath with atleast one electronic unit attached thereto, two in-ear earphones, twocords, one of which connects to one of the in-ear earphone to theelectronic unit, and the other cord connects the other in-ear earphoneto the electronic unit, wherein the two cords are mechanically connectedto the neck-worn sheath, and points of connection of the two cords tothe neck-worn sheath are close to each other and form a dorsal cordconnection node, and are further mechanically connected to each other insections between the in-ear earphones and the dorsal cord connectionnode to form a suboccipital cord connection node at the connectionpoint; and a rear microphone in the suboccipital cord connection node orin the dorsal cord connection node.

Dramatic quality improvement in receiving the user's speech in wearabletelecommunications devices, headsets, wearable multimedia devices,wearable voice-controlled computer devices, hearing aids, etc., isachieved by the invention owing to an innovative configuration of themicrophone array and correlation processing method of the microphonesignals, wherein a microphone array comprising one or more rearmicrophones placed in the dorsal and/or suboccipital node and used asnoise receiver(s) is used for determination of correlated andnon-correlated components of the microphone signals, and wherein thecorrelated components are treated as a noise signal and thenon-correlated components are treated as a target signal, in order toincrease the signal-to-noise ratio of a target signal which is theoutput speech signal of the device.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theadvantages of the invention will be realized and attained by thestructure particularly pointed out in the written description and claimshereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE ATTACHED FIGURES

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 shows a general view of a wearable device according to theinvention in the operational position of the earphones, placed on theuser.

FIG. 2A and FIG. 2B illustrate a mathematical model of the neck surfacewhere a headset has two nodes and the head is shown in the normalposition and may rotate by an angle π/2.

FIG. 3A and FIG. 3B illustrate a mathematical model of the neck surfacewhere a headset has a single node and the head is shown in the normalposition and may rotate by an angle π/2.

FIG. 4A and FIG. 4B illustrate a mathematical model of the neck surfacewhere a headset has two side nodes and the head is shown in normalposition and may rotate by an angle π/2.

FIG. 5A illustrates a mathematical model of the neck surface where aheadset has two nodes and the head is tilted vertically.

FIG. 5B illustrates the calculation of the length of segment AB when thehead is tilted forward by an arbitrary angle α.

FIG. 6A and FIG. 6B illustrate a mathematical model of the neck surfacewhere a headset has a single node and two side nodes, correspondingly,and the head is tilted vertically.

FIG. 7A and FIG. 7B illustrate a mathematical model of a head tiltedsideway where a headset has two nodes and where a headset has two sidenodes.

FIG. 8 illustrates a mathematical model of a head tilted sideways wherea headset has a single node.

FIG. 9 shows dependence of the length of geodesic line AC on the headtilt angle α.

FIG. 10 is a vector diagram of forces.

FIG. 11 is a general view of a wearable device according to theinvention, with neck-wearable housing having a generally U-shape,showing the primary functional components.

FIG. 12A and FIG. 12B show an embodiment of a headset according to theinvention, having a suboccipital node in the form of a clip.

FIG. 13 shows embodiments of a wearable device according to theinvention, wherein the cord portion between the suboccipital and dorsalcord connections nodes is provided in the form of a helical cord.

FIG. 14 shows an embodiment of a headset according to the invention,where the integral cord portion between the suboccipital and dorsal cordconnection nodes is provided in the form of an S-shaped spring.

FIG. 15 shows embodiments of a headset comprising an electronic unit,according to the invention.

FIG. 16 shows an example of electronic components incorporated into theelectronic unit, according to the invention.

FIG. 17 shows an embodiment of a neck-wearable housing connectoraccording to the invention.

FIG. 18 shows an embodiment of a wearable device according to theinvention, with four microphones.

FIG. 19 and FIG. 20 show illustrative circuitry of a headset embodimentaccording to the invention.

FIG. 21A illustrates ideal propagation of a spherical acoustic wavefront when a user speaks.

FIG. 21B illustrates real propagation of a spherical acoustic wavefront, taking in account an acoustic shadow area behind the speakinguser.

FIG. 22A, FIG. 22B and FIG. 22C illustrate equipment connection diagramand disposition of microphones used for experimental measurements of theinvention prototypes.

FIG. 24A shows a schematic diagram illustrating noise canceling in lowfrequency signals, according to the invention.

FIG. 24B and FIG. 24C show schematic diagrams illustrating noisecanceling in high frequency signals, according to the invention.

FIG. 23A shows the difference between amplitude-frequency responsecurves of microphones placed on the chest, in the auricle, and on thedorsal neck surface of a user.

FIG. 23B shows the difference between phase-frequency response curves ofmicrophones placed on the chest, in the auricle, and on the dorsal necksurface of a user.

FIG. 25 shows the position of a rear microphone placed in thesuboccipital node of a wearable device according to the invention.

FIG. 26A shows a schematic diagram of a Wiener adaptive filter accordingto the invention.

FIG. 26B shows a schematic diagram of a least-mean-square method filteraccording to the invention.

FIG. 27 shows a connection diagram of a microphone array comprising arear microphone, in one embodiment of the invention.

FIG. 28 illustrates positions of microphones of a microphone arraycomprising a rear microphone, in one embodiment of the invention.

FIG. 29A illustrates possible positions of a rear microphone on theuser's body in one embodiment of the invention.

FIG. 29B illustrates possible positions of front microphones on theuser's body in one embodiment of the invention.

FIG. 30 illustrates possible positions of front microphones on theuser's body in one embodiment of the invention comprising an additionaldevice in a form of glasses.

FIG. 31 illustrates possible positions of a rear microphone on theuser's body in one embodiment of the invention comprising a dorsal nodeand a suboccipital node, when the user rotates his head

FIG. 32 illustrates position of a rear microphone on the user's body inone embodiment of the invention, when a dorsal node is retracted andattached to a suboccipital node.

FIG. 33 illustrates position of rear microphones on the user's body inone embodiment of the invention, when a dorsal node is detached from asuboccipital node and placed on the user's dorsal surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

In order to assure wearing a device on the user's body withoutadditional support, it is expedient to provide the device in the form ofa loop or a half-loop.

When a user wears a headset with neck-wearable housing having agenerally U-shape (FIG. 1), a node that connects earphone cords 5 to aneck-wearable housing 1 rests on the dorsal surface of the user's neck,in the region of the seventh cervical vertebra. Slightly lower on thehuman body, there is a deepening trough, lying between the spinous andtransverse processes of the vertebrae, sulcus dorsalis, at the level ofthe second—third thoracic vertebrae in the interscapular region, where adepression of various depth of about 4×5 cm (depending on the user'sconstitution and development of subcutaneous fat) is formed at the placeof attachment on the medial edges of both blades of serratus anteriormuscle, and a large and minor rhomboids muscles (musculae rhomboideimajor et minor). The depression may receive a cord winding mechanism andan earphone storage pocket, without projecting above the surface of thebody and so without causing inconvenience to the user.

From the cord connection node on the neck part, the cords run up on thedorsal surface of the neck to the back of the head, on the paravertebraldeepening, sulcus costae vertebralis major, not reaching the outsideoccipital protuberance at the level of the first or second cervicalvertebrae, where an additional cord connection node, suboccipital node6, is appropriate to arrange. If the cords are directed in a V mannerfrom the suboccipital node in the oblique anterior-upward directionslightly above or at the hairline, which is almost coinciding with theupper occipital skull line, through the mastoid regions (regionesmastoideae) of the neck, above the mastoid processes, through theprojection of ligamentum auriclere superior, which attaches the top partof the auricler cartilage to the squamous part of the temporal bone onthe upper portion of the auricle between the front curl and tragus ofthe outer ear to a fixation point in the earphone 3 of the appropriateside.

Then the stable position of the suboccipital cord connection node willbe provided by the availability of fixing anatomical structures at thedatum point, such as the external occipital protuberance and lateraloccipital projections, while a snug fit of the cords on the scalp isprovided by stretching them on the dorsal surface of the head and neckin the places where the cords pass like a girth due to the partialhook-like overlap of the earphone cords through the ligamentum auriclerewith additional fixing of the earphones inside the auricle.

With such attachment only the cords in the portion 7 between nodes 5 and6 are movable, and only this portion may have a slack for compensationof the cord length, which changes when the head turns in the horizontalplane, tilts back, rocks from side to side, as well as when themovements are combined, that is, in all options that can arise in closedkinematic chains of the neck.

Cords 4 are relatively snugly fitted to the scalp and fixed relative tothe user's head, and their length does not vary with all of the abovemovements and varies so little that these variations can be neglected.

Adherence and immobility of the cords 4 between the nodes are alsopromoted by the cellular connective tissue structure of the subcutaneousfat of the occipital region, a minor displacement of the skin in thearea, the presence of Langer's lines running in the transverse directionin the skin, as well as the passage of the cord on a hollow of thepostaural cavity, the hook-like overlap of the cords and positioning theearphones in the outer ear.

In conjunction with the suboccipital node, the tension and absence ofslack are further provided by the design of the earphone, which isplaced inside the auricle, in most cases, without an arc, but having astiff part—an earphone arm attached to the earphone body lying in theouter ear and continued upward from the helical root on the ascendingpart of the helix to the ligamentum auriclere superior, the attachmentpoint of the top of the auricle to the temporal bone.

A flexible cord extends from the stiff arm, leaning over the aboveligamentum auriclere superior at an angle of less than 45°, whichcontributes to the fact that the rigid arm of the earphone forms alever, where at accidental tearing off of the earphone cords, that is,when the cords are pulled at down and back tension vector, the arisingmoment abuts the earphone against the tragus, thereby fixing theearphone between the tragus and the external auditory canal.

It shall be noted that it is preferred to use in-ear earphones, whichare fully or partially inserted into the external auditory canal, incomparison with those in-ear earphones, which are placed within theauricle and are not inserted, wholly or partially, into the externalauditory canal.

In terms of biomechanics, it shall be noted that movements of the headare described on the basis of closed kinematic patterns, andextrapolation of even fairly complex combinations of head movements tothe fixation points can be considered in only one narrative category—aslengthening-shortening the cord portion between the dorsal cordconnection node on the neck-wearable housing and the cord connectionsuboccipital node, which is almost stationary relative to the head andlies under the outer posterior occipital protuberance.

To construct a closed kinematic model, a headset can be represented ashaving two basic parts and a movable connection thereof (FIG. 1).

A first part (head part) is stationary relative to the user's head; ithas two earphones 3, two earphone cords 4 enveloping the auricle fromabove, and a suboccipital node 6.

A second part is stationary relative to the user's body; it has a neckpart 1 and a cord connection node disposed on the neck-wearable housingon the dorsal surface of the neck, a dorsal node 5.

As shown in FIG. 1, positions of the cord connection nodes has beenchosen at reference numeral 5, point A and reference numeral 6, point B(FIG. 2A, FIG. 2B). In this case, the length of the free-hanging cord 7in the portion between the nodes should be minimal.

To determine the length of the AB portion, variations in the distancebetween points A and B as the head turns are to be considered. In thiscase, “distance” is the length of the geodesic line connecting points Aand B on the surface of the neck (FIG. 2B). First, let us define theextension of the cord when the head rotates sideways. Maximum angle ofrotation of the head is 90°. Let us determine the AB distance.

To determine the length of the geodesic line it is necessary to describemathematically the surface of the neck and possible movements of thehead and neck. The neck surface can be represented with sufficientaccuracy as a cylinder (FIG. 2A). Head and neck can make the followingmotions: bending-tilting forward, extension/tilting backward, abductionand adduction/tilting to the left and to the right, turns to the leftand to the right. High movability of the cervical spine is caused by itssegmentation: having a height of about 13 cm, it contains sevenmedium-sized vertebrae and six high intervertebral discs.

Between the first cervical vertebrae and the occipital bone, in theatlantal-occipital joint, adduction/abduction and flexion/extension ofthe head are performed, and between the first and second cervicalvertebra turns of the head to the right and the left are performed. Thejoint work of these joints provides the head movement about three axes.Thus, combined movements of the head and neck are made in relation tothe body, while independent movements of the head are made in relationto the neck. This is because the cervical spine is very flexible, andindependent movements are possible between the first and second cervicalvertebrae.

Let us consider the behavior of the kinematic model of the headset whenthe head rotates in the horizontal plane.

When the head rotates in the horizontal plane, the neck twists mainly inthe region between the first and second vertebrae. Moreover, since thecervical spine is located closer the back of the neck, the twisting axisis also close to the back surface of the cylinder. Since the twisting isperformed only in the upper part of the cylinder about a non-centralaxis, the cylinder surface is distorted. The distortion is most stronglymanifested in the region of the first and second cervical vertebrae,just where point B lies.

The main part of the geodesic line passes below the distortion, so inthe calculations we assume the surface as cylindrical. An importantissue is the determination of the location of point B when the upperpart of the cylinder is twisted to a maximum angle α=π/2. Since ears aresymmetric about the twisting axis, that is the axis of the vertebralcolumn, and the point B is fixed by the tensioned cords in symmetricalposition as well, the position of point B can be expected in the nextcentral angle φ (FIG. 2B).

$\begin{matrix}{\phi = {\arcsin \left( \frac{R - D}{R} \right)}} & (1)\end{matrix}$

The height of point B will not change at rotation either, because it isfixed by the tensioned earphone cords.

Let us consider the task of geodesic line of a cylinder having baseradius R and height h (FIG. 2B). The line passes through twodiametrically opposite points on different basis.

The geodesic line length is

ds=√{square root over (dx ² +dy ² +dz ²)}

shown in differential form.

Since the curve lies on the surface of the cylinder, it is convenient touse cylindrical coordinates, with dx²+dy²=R²dφ², where φ is the polarangle (FIG. 2B). In polar coordinates, the task is to find dependencez(φ), at which the length of the curve is minimal or when the function

$\begin{matrix}{S = {\int\limits_{0}^{\phi_{0}}{\sqrt{R^{2} + z^{\prime 2}}{\phi}}}} & (2)\end{matrix}$

is minimal.

From calculus, a minimum is reached for the curve that satisfies theEuler equation, in this case:

$\begin{matrix}{\left( \frac{z^{\prime}}{\sqrt{R^{2} + z^{\prime 2}}} \right)^{\prime} = 0} & (3)\end{matrix}$

It follows that z′(φ)=a, where a is the constant factor, thenz(φ)=a×φ+b. Coefficients are determined though boundary points A(R,0,0), the attachment point of the lower clip, and B (R,φ0,h) with thepolar angle φ=0 being at point A and equal to φ₀ at point B. Then thecoefficients are of the form: a=h/φ₀, b=0. Then z(y)=φ×h/φ₀. And thelength of the curve is equal to the value of the functional, i.e.:

$\begin{matrix}{S = {{\int\limits_{0}^{\phi_{0}}{\sqrt{R^{2} + {h^{2}/\phi_{0}^{2}}}{\phi}}} = \sqrt{{\phi_{0}^{2}R^{2}} + h^{2}}}} & (4)\end{matrix}$

Thus, variation in distance AB or movability of cords ΔS is:

ΔS=√{square root over (h ² +R ²φ₀ ²)}−h  (5)

where R—the radius of the cylinder, φ₀—the angle of rotation of node B,defined relative to the central axis of the cylinder, h—the height ofthe node. With regard to expression (1) the expression for movability ofthe cords is:

$\begin{matrix}{{\Delta \; S_{t}} = {\sqrt{h^{2} + {R^{2}{\arcsin^{2}\left( \frac{R - D}{R} \right)}}} - {h.}}} & (6)\end{matrix}$

Now, for comparison, we will consider variation in the length of cordsat horizontal rotation of the head in conventional headsets. FIG. 3Ashows an example of such a headset. In this case, cords are clamped atpoint A, and the movable part is the entire cord from point A toearphones disposed at points C and D.

Conventionally, the headset is denoted as a single node headset. Thus,movability of the cords can be determined from the difference betweenthe distances from point A and D when the head rotates at the angle of90° in one direction and in the other direction, since while thedistance or the geodesic line length increases in one direction, itdecreases in the other direction. These two distances can be determinedin FIG. 3B, where the minimal distance is the length of line AC, and themaximum distance corresponds to line AD. As a result, movability of thecords can be found from expression (5) with the assumption of h=H andφ₀=π, and it has the form:

ΔS _(t1)=√{square root over (H ² +R ²π²)}−H  (7).

Let us consider another type of a headset, which will be conventionallycalled a headset having two side nodes (FIG. 4A). In this case assumethat the headset cord, at rotation, always passes through points at thebase of the cylinder, i.e., points A and B, cord connection nodes. Thenthe minimum distance between points A and C or B and D is H. The maximumdistance when the head is rotated to 90° is shown by geodesic lines ACand BD (FIG. 4B). As a result, movability of the cords is alsodetermined from expression (5) with the assumption of h=H and φ₀=π/2,and is defined by the following expression:

ΔS _(t2)=√{square root over (H ² +R ²π²/4)}−H  (8).

Next, let us consider behavior of the kinematic model when the headtilts forward and backward in the vertical plane.

Tilts of the head are performed by rotation of the head around the axisextending between the first cervical vertebra and the occipital bone.The tilt is often accompanied by a tilt of the entire cervical spine. Ina headset having two nodes, the tilt of the neck has a little effect ondistance AB, but rotation of the head has a significant impact, sincenode B is disposed directly on the occipital part. Thus, knowingdistance from B to axis of rotation r and angle of rotation α (FIG. 5A),shift of node B can be estimated as

BB ₀ =rα  (9).

Now we will obtain an expression for the length of segment AB atarbitrary angle α from the triangle AOB (FIG. 5B):

AB ² =AO ² +r ²−2AO×r×cos(α+β)  (10).

Distance to axis r can be determined though the distance from the backsurface of the neck to the center of the cervical spine, i.e., R-D, andthe difference of heights of point B and the axis of rotation of thehead h₀:

r=√{square root over ((R−D)² +h ₀ ²)}  (11).

Then we will obtain the following expression from triangle OO₁A:

AO=√{square root over ((R−D)²+(h+h ₀)²)}  (12).

Expression for angle β can be obtained from expressions (10), (11) and(12) by substituting α=0, AB=h.

$\begin{matrix}{\beta = {\arccos {\frac{\left( {R - D} \right)^{2} + {hh}_{0} + h_{0}^{2}}{\sqrt{\left( {\left( {R - D} \right)^{2} + \left( {h + h_{0}} \right)^{2}} \right)\left( {\left( {R - D} \right)^{2} + h_{0}^{2}} \right)}}.}}} & (13)\end{matrix}$

Thus, the expression for AB has the form:

$\begin{matrix}{{{AB}(\alpha)} = {\sqrt{\begin{matrix}{{2\left( {R - D} \right)^{2}} + \left( {h + h_{0}} \right)^{2} + h_{0}^{2} -} \\{2\sqrt{\left( {\left( {R - D} \right)^{2} + \left( {h + h_{0}} \right)^{2}} \right)\left( {\left( {R - D} \right)^{2} + h_{0}^{2}} \right)}{\cos \left( {\alpha + \beta} \right)}}\end{matrix}}.}} & (14)\end{matrix}$

In case of tilting, the head backward expression (14) is no longer true,because there is no tension of the skin and soft tissues of the dorsalpart of the neck. In this case it is appropriate to estimate distanceBB0 as the difference between heights of points B and B₀:

Δh=r(cos(γ₀+α)−cos γ₀)  (15).

As a result, movability of the cords is calculated from expression (14)by substituting α=α_(m) (maximum tilt angle), and (15) by substitutingα=−α_(m):

ΔS _(c) =AB(α_(m))−√{square root over ((R−D)² +h ₀ ²)}(cos(γ₀−α_(m))−cosγ₀)  (16).

Apparently, α_(m) cannot exceed γ₀ due to the limit on deformation ofthe neck. To assess movability of the cords, we may assume α_(m)=γ₀,then with regard to expression (14) we may obtain:

ΔS _(c) =AB(γ₀)−√{square root over ((R−D)² +h ₀ ²)}(1−cos γ₀)  (17).

In case of headsets with a single node or with two side nodes rotationin the vertical plane affects the height of points C and D. Variation inthe latter, Δh₀, can be determined if relative distance r₀ between axisCD and the axis of rotation, as well as angular position α₀ of the axesare known (FIG. 6A):

Δh ₀ =r ₀(cos α₀−cos(α₀+α))  (18).

As a result, variation in the distance or movability of cords for aheadset having a single node can be obtained from expression (4) withH−Δh₀ set instead of h and φ=π/2. In this case, angle α varies in therange −α_(m)<α<α_(m), and the height varies in the range:

Δh ₀₁ =r ₀(cos α₀−cos(α₀−α_(m)))<Δh ₀ <r ₀(cos α₀−cos(α₀+α_(m)))=Δh₀₂  (19),

ΔS _(c1)=√{square root over ((H−Δh ₀₁)² +R ²π²/4)}−√{square root over((H−Δh ₀₂)² +R ²π²/4)}  (20).

FIG. 6B illustrates the case of a headset having two side nodes.Movability of the cords can be estimated through variation in heights ofpoints C and D. Then, from expression (19) we can obtain movability ofthe cords in the following form:

ΔS _(c1) =Δh ₀₂ −Δh ₀₁  (21).

Like in the case of a headset having two nodes, estimates α_(m)=γ₀=α₀are true. Then we may obtain the following estimate for movability ofcords:

ΔS _(c1)=√{square root over ((H+r ₀(1−cos γ₀))² R ²π²/4)}−√{square rootover ((H−r ₀(cos γ₀−cos 2γ₀))² +R ²π²/4)}  (22),

ΔS _(s2) =r ₀(1−cos 2γ₀)  (23).

Also consider behavior of the kinematic model when the head tiltssideway in the vertical plane.

When the head tilts sideway, the movement of the head can be representedas rotation of the upper part of a cylinder about axis s, which extendsapproximately through point O of intersection of axes t and c.

In the case of a headset having two nodes, such rotation is accompaniedby a shift of point B, which can be estimated through the distance toaxis of rotation O₁B₀ (FIG. 7B). As seen in FIG. 7B: O₁B₀=h₀. Todetermine the length of AB it is necessary to determine horizontal shiftΔs and vertical shift Δh of point B, because AB=√{square root over((h+Δh)²+Δs²)}. In this case Δh=h₀(1−cos α) and Δs=h₀ sin α. Thenmovability of section AB when the head tilts sideway, will be changed tomaximum angle α_(m):

ΔS _(s)=√{square root over ((h+h ₀(1−cos α_(m)))² +h ₀ ²sin²α_(m))}−h  (24).

Now let us consider the case of a headset having side nodes. In thiscase, variation in segments AC and BD can be accounted for byconsidering the shift of points C and D on arcs of circle from points C₀and D₀. The length of AC in the case of the head tilt shown in FIG. 7Bcan be found as:

AC=AC ₀ +R _(s) α=H+R _(s)α  (25).

Here R_(s) is the radius of rotation path about axis s, which can befound from triangle COO₂, where OO₂ can be found, given that the heightof point O is h+h₀ (FIG. 5B), then OO₂=H−h−h₀, and CO₂=R, therefore:

CO=R _(s)=√{square root over ((H−h−h ₀)² +R ²)}  (26).

To determine BD, only variation in the height of point D, ΔH=R_(s) sinα, should be taken into account because the cord in this area is loose:

BD=H−ΔH=H−R _(s) sin α  (27).

Considering maximum deflection angle α_(m)=45°, the following expressioncan be obtained for movability of cords:

ΔS _(s2) =R _(s)α_(m) +R _(s) sin α_(m)  (28).

Now we will consider the case of a headset having a single node (FIG.8). In this case, the calculation is more complicated and requiresspecial treatment for the length of geodesic line AC. In this task thesurface of the neck can be described as a surface of an inclinedcylinder. To do this, let us find the angle of inclination of thecylinder surface, β. From triangles BCC₀ and OCC₀ we may find CC₀=2R_(s)sin(α/2):

BC=√{square root over (H ²+4R _(s) ² sin²(α/2)−4HR _(s)sin(α/2)sin(α/2−γ))}  (29).

From triangle BCC₀ we may obtain:

BC/sin(π/2−a/2+γ)=2R _(s) sin(α/2)/sin β

so we may obtain:

β=arcsin(2R _(s) sin(α/2)cos(α/2−γ)/BC)  (30).

Here

γ=arctan(R/(H−h−h ₀))  (31).

Therefore,

AC=√{square root over ((BC(1−sin β))²+π² R ² cos²β/4)}  (32).

It should be noted that, taking into account the dependence of BC and βon angle α from equations (29) and (30), we can expect a non-monotonicdependence of the line length AC(α). FIG. 9 shows this dependence forparameters listed in Table 1. It can be seen that AC reaches maximumAC_(max)=16.6 cm at angle α₀=8.6°.

Now let us find the length of AD as this line describes the minimumlength of the cord. In this case we may consider that the height of thecylinder has changed to ΔH=R_(s) sin α, then using the expression (27)we may obtain:

AD=√{square root over ((H−R _(s) sin α)²+π² R ²/4)}  (33).

As a result, movability of cords ΔS_(s1) is determined as the differenceof the lengths of lines AC_(max) and AD at the maximum angle ofinclination, α_(m):

ΔS _(s1) =AC _(max)−√{square root over ((H−R sin α_(m))²+π² R²/4)}  (34).

Table 1 shows the comparison of cord movability for various types ofheadsets. As seen in the table, a headset having two nodes, that is, aheadset in which two earphone cords are connected to the neck-wearablehousing through a dorsal cord connection node in close proximity to eachother and have an additional point of fixation to each other, i.e., asuboccipital node; the cords have the lowest movability as compared withconventional headsets. This advantage applies to all kinds of movementsof the head.

Comfortable wear of the headset is determined by the maximum possiblemovability of cords, respectively, the difference between the minimumand maximum possible length of a loose cord, arising at differentpositions of the head. In a headset having two nodes, the maximum lengthis determined by maximum distance AB between the nodes, that is, thelength AB defined in expression (14). In a headset having a single node,the maximum length of the cord is achieved when the head rotates to 90°:

L _(max 1)=√{square root over (H ² +R ²π²)}  (35).

For a headset having two side nodes we may obtain the maximum lengthwhen the head tilts sideway:

L _(max 2) =H+R _(s)α_(m)  (36).

Table 1 contains numerical estimates, from which it follows that theheadset having two nodes has a minimum length of a maximum extended, butslack portion of cord. It should also be noted that the estimatesobtained for a headset having two side nodes have been deliberatelyreduced because cords passing from points A and B to the transceiver arenot taken into account, and account of them would significantly increaseL_(max2).

Therefore, the availability of two optimally positioned nodes A and Bcontributes not only to reduction in slacking of the cords, but alsoprovides tension of the cords extending from node B to earphones. Sincethese cords lie on the curved surface of the neck, the tension creates apressure on the skin (FIG. 10). As a result of this pressure therearises a friction force of the cord against the skin and a pressureforce of the suboccipital cord connection node, node B, against softtissues, while the difference of vectors of these forces leads tofixation of the cords on the scalp and further secures earphones in theauricle. Thus, the securing force is concentrated not only on theauricles, and not only by fixing the earphones in the external auditorycanal, but it is uniformly distributed over the entire length of thecord, which greatly facilitates wearing of the earphones. Node B, i.e.,suboccipital cord connection node, is held in a stable position owing tothe uniform distribution of various forces that arise in the occipitalregion at the specified arrangement geometry of the cords and theirmutual coupling, taking into account human anatomical features.

FIG. 10 shows a vector diagram of projections of the forces acting onthe suboccipital cord connection node, node B. Node B is fixed throughtension of the cords. Thin arrows indicate tensile forces of the cords,the total of which creates pressure on the skin. As a result, node Bundergoes a force of reaction of the skin and surrounding tissues,indicated by wide hollow arrow, that seeks to move the node down, andthe arising forces of friction against the cord, marked with wide solidarrow, fix the position of node B. In this model, the tension of cordsbelow the node was neglected, as its length has been chosen for optimaland the cord is loose, and it has an excess length of about 9.8 cm toensure movability of the cords in movements of the head and neck.

Table 1 summarizes results of comparison of cord movability and maximumcord length in headsets with different geometries.

TABLE 1 Comparison of movability and maximum length of cord in headsetswith various geometry Movement Rotation of head Tilt of head Tilt ofhead in horizontal plane forward/backward sideway Estimate at Estimateat Estimate at Headset type Expression parameters Expression parametersExpression parameters Headset with (6) R = 6.5 cm, (12) R = 6.5 cm, (24)R = 6.5 cm, two nodes h = 6 cm, h₀ = 2 cm, h = 6 cm, D = 1 cm, D = 1 cmh₀ = 2 cm α = 90° = 1.6 rad ΔS_(c) = 8.6 cm α_(m) = 45° = 0.8 rad ΔS_(t)= 2.9 cm ΔS_(s) = 0.6 cm L_(max) = 9.8 cm (see expression (14)) Headsetwith (7) R = 6.5 cm, (18) r₀ = 3 cm, (34) R = 6.5 cm, a single node H =13 cm γ₀ = 45° h = 6 cm ΔS_(t1) = 12.5 cm ΔS_(c1) = 2.2 cm h₀ = 2 cmα_(m) = 45° = 0.8 rad ΔS_(s1) = 3.4 cm L_(max 1) = {square root over(H² + R²π²)} = 25.5 cm Headset with (8) R = 7 cm, (19) r₀ = 3 cm, (28) R= 6.5 cm, two side nodes H = 13 cm γ₀ = 45° h = 6 cm ΔS_(t2) = 5.2 cmΔS_(c2) = 3 cm h₀ = 2 cm α_(m) = 45° = 0.8 rad ΔS_(s2) = 11 cm L_(max 2)= H + R_(s)α_(m) = 19.4 cm

The technical effect provided by the invention includes the ability toreduce the length of the movable portion of the cords between theearphone and the neck-wearable housing, and the adherence of thestationary portion of the cord to the surface of the user's body andfixation of the stationary portion by tension, to substantiallyeliminate slack of the cords connecting the earphones with theneck-wearable housing, which in turn, prevents breakage of cords orearphones, and provides an additional opportunity for constant wear ofthe headset by the user in the operational position or with theearphones taken off, because the cords do not impair the aestheticappearance of the user when the earphones are worn in the operational ornon-operational position. Furthermore, a mechanism for full or partialwinding up the earphone cords when not in use can be arranged on theheadset more easily.

A headset for a mobile electronic device (FIG. 1, FIG. 11) comprises aneck-wearable housing 1 having a generally U-shape with at least oneelectrical connector 2 attached to it; two in-ear earphones 3A, 3B; twocords 4A, 4B, each connected at one end to a corresponding in-earearphone and connected at its other end to the electrical connector andthese the two cords are mechanically connected to the neck-wearablehousing 1, and points of connection of the cords to the neck-wearablehousing are in close proximity to each other and form a dorsal cordconnection node 5. They are also mechanically connected to each other insections between the in-ear earphones and the dorsal cord connectionnode 5 to form a suboccipital cord connection node 6 at the connectionpoint.

When the headset is worn in the operational position, the dorsal cordconnection node 5 and the suboccipital cord connection node 6 arelocated on the dorsal surface of the neck, and cords 4 in sections 7between the earphones 3 and the suboccipital node 6 are located over anauricle.

In various embodiments (FIGS. 12A, 12B) the suboccipital cord connectionnode may be a clip 8, and the length of the cords can be adjusted bymoving the clip along the cords. Also, the suboccipital node may includean electrical connector to disconnect the cords.

At least one cord in the section 7 between the suboccipital and dorsalnodes can be configured as a helical spring. In the embodiment shown inFIG. 13, the section 7 between the suboccipital and dorsal cordconnection nodes is configured in the form of a helical cord and acts asa tension spring. The cords may be formed not only in the form of ahelical spring, but also in the form of a flat S-shaped spring, whichmay be more expedient in some cases, as this allows avoiding distortionof the spring and provides a precisely adjacent position of thesuboccipital node in relation to the device when the earphone is in thenon-operational position.

An embodiment of the headset using an S-shaped spring is shown in FIG.14.

In preferred embodiment (FIG. 15), a headset comprises at least oneelectronic control unit 9 mechanically and electrically connected to anelectrical connector. The electronic unit 9 can be placed on the chestat one side of a neck-wearable housing. The electronic unit 9 maycomprise a signal transceiver, such as Bluetooth, to receive signal froma cell phone; there may further be a battery, a player, a radio, a USBflash drive, an electronic key, a satellite signal receiver such as GPSand/or GLONASS receiver able to tell coordinates through voiceinformation transmitted directly to the user's earphones.

FIG. 16 shows possible electronic components incorporated into theelectronic unit 9. The electronic unit 9 communicates with a mobilephone, a satellite navigation system, a computer or a mobile station viaa radio communications module 10. A signal processor 11 processes audiosignals, and controls and manages data streams. Digital-to-analogconversion and amplification of a signal, and volume control areperformed by a codec or an audio module 12. A memory module 13 storescontrol software, hardware setting profiles and user's information. Apower source, such as a battery 14 incorporated in the electronic unit 9and/or disposed on the neck-wearable housing, provides operation ofmicrocircuit chips. The electronic unit 9 may include control buttons,such as 15, 16, and 17. A short-range Near Field Connection module 18can be used for data exchange and quick coupling with a mobileelectronic device.

In various embodiments of a headset the electronic unit 9 accommodatesthe following accessories: an extra controller 19 for processing signalsfrom control buttons; a slot 20 with a connector to connect an externalflash memory, a USB connector 21 for data transfer or charging thebattery. Connectors 22 are used to connect earphones, externalmicrophones, and additional control buttons.

Buttons 15, 16 can be disposed on the neck-wearable housing 1 (FIG. 15).

In various embodiments of the headset, control buttons and keys aredisposed both on the housing of the electronic unit 9 and theneck-wearable housing.

Furthermore, pressure can be made at once on two opposite buttons withtwo fingers, thumb and forefinger, simultaneously on both sides of theneck-wearable housing relative to the electronic control unit or therigid member disposing on the neck loop. This eliminates accidentalpressure by a vehicle safety belt, a bag strap, etc. Such an arrangementof buttons provides for maximum accessibility to them, even when wearinga tie, suit or coat.

The headset (FIG. 15) may further comprise a rigid member 23 areconfigured like shells having a polyhedron-like shape, wherein a planesof two narrow facets of the polyhedron-like shape are substantiallyparallel to each other and substantially perpendicular to the user'sbody plane, and the rigid member contains a button 17 positioned on thefacets near the rigid member's corner where the facet borders anotherfacet being perpendicular to the user's body plane, and the button isconfigured to be easily found and activated through the clothes when thedevice is worn under the clothes, wherein intentional activation thereofis possible by catching and holding the member with two fingers.

Herein, control means of the claimed device are mainly described asbuttons or keys in examples and embodiments. However, other types ofcontrol means may be used depending on the functions controlled by thesecontrol means.

In an embodiment of the headset (FIG. 15), a power supply 24 and amicrophone 25 can be disposed on a neck-wearable housing 1, for examplein a rigid member 23. The power source (e.g., batteries) may bedistributed in the electronic unit 9.

In an embodiment of the headset (FIG. 18), four microphones 17A-D can bedisposed on a neck-wearable housing 1 forming a microphone array.

In some embodiments, the headset can be free of cords transmittingsignal to the earphone and have a power cord only; a cordless module ineach earphone to receive and transmit electromagnetic signal for theearphone.

A neck-wearable housing 1 (FIG. 17) may have at least two slots 26 forconnecting additional sections of the neck loop.

FIGS. 19, 20 show a connection circuitry of keys and microphones in oneembodiment of the headset. This embodiment includes twelve keys andseven microphones.

Data outputs to contact members, sync signal inputs of the microphonesand control keys are connected to inputs of a signal processor orcontroller 27 (FIG. 20). Earphones are connected to a control chip,CODEC 28, or an audio module, which comprises a digital-to-analogconverter, and a controllable-gain amplifier. In operation, theprocessor data exchanges data with peripheral devices 29 as well. FIG.19 shows electrical circuitry of the headset.

Unlike known stereo Bluetooth headsets, the electronic necklace in theform of an open or a closed loop can be controlled directly through theclothes, with no necessity of pulling it from a pocket of a bag ordrawing it from under the clothes.

The headset may also comprise gyroscopes, accelerometers, magnetometersor other position sensors to assist in navigation with voice prompts ofGPS device.

Benefits of the invention including: shortening by more than two timesthe length of the movable parts of cords, i.e., the portions between thenodes; convenient position and tension of cords on surface of the body;and immobility of the remaining cord portions allow the headset to beworn under clothes in the operational and non-operational position, andthroat microphones may be disposed thereon.

In many embodiments the headset can be controlled without taking it fromunder the clothes or pulling a phone from a pocket, because the buttonslocated under clothes can be pressed from outside, over clothes, or bygiving voice commands without hand manipulations at all. Direct contactbetween the device and the user's skin allows positioning on the headsetsensors for monitoring the state of user's health, such as temperature,blood pressure, sugar, alcohol in skin secretions, etc., to monitorgalvanic skin response for the purpose of control of the sympatheticnervous system, which allows using the headset as a part of abiotelemetry system for medical diagnostics.

The headset can be used not only as an option for connecting to a mobilephone or itself used as a mobile phone, but also as a component of awearable mobile system with hardware distributed over several devicescarried by a person, for example, some of hardware and battery base canbe accommodated in a man's trouser belt, while the wired connection tothe headset can be implemented in a cord, which lies under the clothesalong the user's spine on the back; the headset itself can implementfunctionality of a mobile phone or smartphone, while a separately wornscreen/keyboard unit can be used as a wireless interface to the mobilephone or smartphone.

The headset design comprising a suboccipital cord connection node and ashort, as compared to the other neck headsets, section of the movableportion of cords connecting the headset with the neck-worn housingallows wearing the headset under user's clothes, thereby eliminating theuse of external microphone close to the user's mouth. This leads to theneed to provide a special arrangement topology of microphones in theheadset and a hardware/software system for processing signals frommicrophones.

The problem of noise reduction in speech signals became even morepressing as the wearable devices may be used in a very noisyenvironment.

Speech of a human being is a mix of tones with a lot of harmoniccomponents and various noises, which mix very fast changes in time. Themost representative frequency range of the human speech is 250 to 3000Hz. The wave front of the sound is commonly spherical with the center ofthe sphere located at the speaker's mouth (FIG. 21A). The waves tend topropagate in all directions; however the real propagation model dependson the acoustic environment and the diffraction and interference patternwhich in turn depends on the wavelength.

The waves corresponding to speech components over 2000 Hz are almostunable to pass around the human head (which dimension is about 21 cm),so a so-called “acoustic shadow” is formed in the area of the occipitalsurface and the dorsal neck surface of the user (FIG. 21B). Lowerfrequency sounds below 340 Hz having the wavelength of 1 m and more areable to pass around the human head and reach the occiput area at thecost of some amplitude decrease.

An anthropometric dummy was used in the acoustic field researchperformed by the inventor. FIG. 22A illustrates equipment connectiondiagram, where the test setup comprises an artificial voice unit 30(Bruel & Kjaer, type 4128) connected to a power amplifier 31 (Bruel &Kjaer, type 2636), a number of microelectromechanical system (MEMS)microphones 33-38 (Knowles, type SPH1642HT5H-1) connected to apreamplifier 32 (Bruel & Kjaer, type 1054), and a measurement unit 2(Audiomatica, CLIO) connected to a computer. FIG. 22B and FIG. 22Cillustrate disposition of the microphones on the dummy's surface.

A variable frequency sinusoidal signal was supplied from the measurementunit 39 via the power amplifier 31 to the artificial voice unit 30. Themicrophones 33-38 were alternately connected to the measurement unit 39via the preamplifier 32. A quiet room was used for the measurements anda gain-frequency characteristic and a gain-phase characteristic weredetermined for each of the microphones.

Irregularity of the obtained gain-frequency characteristics is mostlycaused by frequency features of the artificial voice unit. As relativecharacteristics measured in the target points were in the experimentfocus, the irregularity may be neglected. The front microphone 36 wasused as a main microphone, and an additional reference microphone (notshown in the figures) disposed in front of the dummy's mouth was used inorder to determine the relative characteristics of the microphones33-38.

The experiments yielded the following results (FIG. 23A, FIG. 23B):

-   -   the directional diagram of the artificial voice unit 30 was        found mostly even in the frequency range below 2 kHz and        substantially uneven in the frequency range above 2 kHz, while        the most sharp unevenness was found in the region of 10 kHz and        more;    -   the most difference (20 dB) in the frequency range above 2 kHz        was found between the gain-frequency characteristics of the main        microphone 36 centrally positioned on the dummy's chest and the        rear microphones 37, 38;    -   a moderate difference of 5 to 10 dB in the frequency range above        2 kHz was found between the gain-frequency characteristics of        the microphone 33 positioned near the dummy's auricles and the        rear microphones 37, 38.

It is known that increasing signal-to-noise ratio (SNR) just by 1 dB isable to improve the speech intelligibility, which is usually evident toexperts during experiments and being beyond possible experimental errorrange.

Thus, the main microphone 36 positioned on the dummy's chest providesmaximum level of a speech signal comparable with the referencemicrophone level, while the microphones 37, 38 positioned on the dummy'socciput or dorsal neck area provides minimal level of the speech signalin the frequency range above 2 kHz. This frequency range is particularlyimportant for correct transmission of the speech via communicationschannels, as harmonic components providing the voice personalizationmostly occupy the range over 1.7 kHz. Therefore, a pair of microphones,one of which is located on the user's chest and the other one is locatedon the back part of the user's neck, may be used for separation of thetarget speech signal.

This is apparent from the above data, that positioning a microphone inclose vicinity of the user's auricle (like the microphone 33), providessubstantially less speech amplitude difference between this sidemicrophone and the front microphone (like the main microphone 36), thanthe difference between a rear microphone (like the microphones 37, 38)and the same front microphone.

Most of the above-mentioned conventional solutions use a frontmicrophone located close to the user's mouth (like a boom microphone),so the speech amplitude difference is greater than indicated in theabove experimental data. However, when a microphone is aggregated withan earphone, some special solutions for preventing acoustic feedbackbetween the microphone and the earphone have to be used, which makes thedigital signal processing algorithm for noise reduction more complicatedand less efficient.

Therefore, the inventor worked on finding an optimal number and layoutof microphones applicable to a neck-worn hands-free device and selectingthe best processing method for noise reduction.

Different noise reduction systems are used for increasing SNR of speechsignals. The general principle of these systems is determination of anoise estimation for a source additive signal by mathematical methods,and further subtraction of the noise estimation from the additivesignal. Functions of noise reduction algorithms applicable to amicrophone array are shown in FIG. 24A and FIG. 24B, wherein dedicatedmicrophones for receiving noise are used.

One possible method is illustrated by FIG. 24A, wherein the noise signalu_(n) obtained from a dedicated noise microphone is subtracted fromsignals u₁ . . . u_(m) obtained from another microphones located in thearea of direct propagation of a speech sound wave. Further, the outputsignal u_(s-n) is formed by the unit 39 from the subtraction results.

In another method illustrated by FIG. 24B, spectrum-sensitivesubtraction is performed, which takes into account the phase differenceof the microphones, which difference is significant for high frequencysignals. In this method, signals of all of the microphones areFourier-transformed, afterwards the noise amplitude n is subtracted fromsignal amplitudes s₁, . . . s_(m) and the output signal u_(s-n) isformed by the unit 39 from the subtraction results. The algorithmimplies dividing the working bandwidth into a number of sub-bands andusing individual weight factors for the noise signal u_(n) and for theprocessed signals u₁ . . . u_(m) in each sub-band in order to form theoutput signal u_(s-n). Different embodiments of this method may be donelike those disclosed in references [6], [7]. For instance, Fast FourierTransformation (FFT) and correlation matrices may be used, like in aWiener filter.

The above methods are applicable when the microphones are located in thearea of direct sound wave propagation, i.e., in an area where the wavefront is ideally spherical.

FIG. 24C shows a simplified embodiment of the method of FIG. 24B,wherein one of two front microphones is used as a noise microphone, andthe other one is used as a main microphone. The unit 39 selects the bestmicrophone and controls the switch 40, where the target signal level ofthe best microphone is higher by a predetermined threshold 41.

The noise sources are usually distantly located so the distance betweenthem and the microphones is far greater than the sound wavelength.Therefore, the acoustic pressure S in the wave is fairly defined by thespherical wave formula:

$\begin{matrix}{{s = \frac{A\; {\exp \left( {{- }\; {k_{s}\left( {r - {vt}} \right)}} \right)}}{r^{2}}},} & (37)\end{matrix}$

where A is the oscillation amplitude of the source, k_(s) is the wavevector, v is the wave speed, r is the sphere radius, t is the time ofpropagation.

It can be seen from the above expression that if the user's headdimensions are substantially less than the distance r, the wave may beconsidered flat and the amplitude may be considered constant. In thiscase, the noise signal amplitude is about the same for each of themicrophones disposed in a neck-worn device. Moreover, in a room, thenoise sound waves may be highly reverberated so the noise sound wavefront may be gravely distorted. This means that the noise signal levelof all the microphones is substantially equal, no matters which side amicrophone is directed to. So it may be enough to simply subtract thesignal of the rear microphone used as a noise microphone from the signalof the front microphone used as a main microphone. If a microphone arrayis used, the subtraction may be performed for signals u₁ . . . u_(m)obtained from all microphones except for the noise microphone (FIG.24A).

However, such a simple subtraction method does not take in account thephase incursion between the noise microphone and the other microphones.This difference may be substantial for high frequencies, when thedistance between the microphones is comparable to the sound wavelength.In this case, the spectrum-sensitive subtraction may be used as shown inFIG. 24B.

When possible, one or several front microphones may be positioned in adevice worn on the user's head (like a helmet, glasses, massiveheadphones, etc.). If not, it is expedient to locate a front microphonein a wearable neckband, so that the microphone is positioned in the areaof the joining point of clavicle and episternum. A couple of frontmicrophones (a left front microphone and a right front microphone)located on the user's chest can be used in order to compensate theuser's head rotation during the talk. In particular, signal phase andamplitude differences tend to occur due to the user's head tilt androtation, as the distance between the user's mouth and the frontmicrophones continuously varies and a kind of a comb filter is formed.

A microphone signal adder may be used for forming a single front soundsignal by addition of the signals obtained from the front microphones.Additionally, a dynamic range compressor (DRC) may be used for reducingthe excessively wide dynamic range. These solutions have been describedin the prior art, so their details are omitted for the sake of brevity.It just shall be noted that these solutions are quite rarely used inwearable devices, as they require a hardware having substantialdimensions, weight and power consumption, whereas the necklaceform-factor easily allows using such solutions.

The controlled switch solution of FIG. 24C is also applicable forselecting one of the two front microphones, depending on which side theuser's head is rotated and/or tilted is. Preferably, directionalmicrophones may be used as the front microphones, wherein thedirectional diagram of each microphone is headed up to the user's mouth.A dedicated phased microphone array or a gradient microphone array maybe used instead of the directional microphones, which may be e.g., acouple of front microphones positioned on the central line, comprisingan upper microphone placed closer to the user's mouth and a lowermicrophone placed farther to the user's mouth).

The microphones shall be relatively fixed on the wearable device. ABowden cable may be used for connecting members of the wearable devicein order to prevent twisting thereof and flipping over the microphones.Rustle in the microphones may be reduced (not eliminated though) byusing very smooth cases for the wearable device members and by noiseinsulation of the microphones within the cases. The microphone holesshall be placed in those faces of the wearable device members, which donot normally contact the user's clothes.

The position of the noise microphone is stipulated by the pattern ofacoustic field formed during the user's speech. In particular, thespeech wave level is expected to be substantially lower near the backside of the user's neck (FIG. 21B) due to diffraction effect and thewave is expected to be delayed. This assumption is confirmed by theabove-mentioned experimental data.

Moreover, as can be seen in FIG. 23A, the gain-frequency characteristicsare non-monotonic. This may occur due to acoustic wave interferenceand/or resonance effects in the sound source and the environment.However, as the general pattern of the gain-frequency characteristics issubstantially the same, unevenness of the characteristics may beneglected and the signal level differences of different microphones maybe considered. In particular, using the microphones 37, 38 as the rearmicrophones is preferable, because the microphones 37, 38 provide lesslevel of the user's speech signal than the microphone 33 and facilitatemore distinct separation of the environmental noise signal.

In order to more clearly define the impact of the acoustic wavediffraction, the phase-frequency characteristics of the microphonesshall be analyzed. The phase difference of sound oscillations for twomicrophones is the product of the wave vector k_(s) and the distance lbetween the microphones:

Δφ=k _(s) l  (38).

If the acoustic wave interference is neglected, then the acoustic wavedispersion principle is:

ω=vk _(s)  (39),

where v is the wave speed. Combination of (38) and (39) yields theexpression for the phase difference:

Δφ=ωl/v  (40).

Thus, a linear dependence for the phase difference of sound oscillationsfor two microphones can be expected with the above assumptionsapplicable for low frequency. However, these assumptions are generallynot valid in the frequency range over 2 kHz. This is illustrated in FIG.23B, where the phase-frequency characteristic of the main frontmicrophone 36 is nearly linear, while the phase-frequency characteristicof the rear microphone 37, 38 is substantially non-linear, and thelinearity measure of the phase-frequency characteristic of the sidemicrophone 33 is intermediate. Linearity of the phase-frequencycharacteristic may be defined as the dependence of the acoustic path onthe frequency l(ω). This dependence may be caused by the curving thesound wave front due to diffraction on the user's head.

To sum up, the analysis results show the following:

(a) the microphones 34, 35, 36 provide maximum SNR in the frequencyrange below approximately 1.5 kHz and they are optimal for use as themain microphones;

(b) the microphones 37, 38 provide minimal SNR in the frequency rangeover approximately 1.5 kHz and they are optimal for use as the noisemicrophones;

(c) the microphones 33 provide intermediate SNR in the frequency rangeover approximately 1.5 kHz and they are not optimal for use as the noisemicrophones.

This means that when speech information is received with no backgroundnoise, the microphones 34-36 provide the best quality of the targetsignal. The microphones 37, 38 provide the target signal withsubstantially depressed level and shifted phase in the frequency rangeover approximately 1.5 kHz, comparatively to the microphones 34-36.

When diffused noise is received from a distant source and/or when thenoise is received in a room where reflections occur, the levels of thenoise signal obtained from each of the microphones are approximatelyequal. In other words, by placing the noise microphone on the back partof the user's neck, it is possible to obtain a signal having minimalcontent of the diffracted speech sound and about the same noise contentas the main microphone. This facilitates further processing the signaland separating the noise content in order to provide desired SNR of thetarget signal.

FIG. 15 and FIG. 25 shows a wearable telecommunication device,comprising a neck-wearable housing 1 with an electronic unit 9 attachedthereto, two in-ear earphones, two cords 4A, 4B, one of which connectsto one of the in-ear earphone to the electronic unit, and the other cordconnects the other in-ear earphone to the electronic unit; and amicrophone array for picking up and processing a user's voice, themicrophone array comprising a front microphone 25, a rear microphone 37and a processor, wherein the two cords are mechanically connected to theneck-wearable housing, and points of connection of the two cords to theneck-wearable housing are close to each other and form a dorsal cordconnection node 5, and are further mechanically connected to each otherin sections between the in-ear earphones and the dorsal cord connectionnode 6 to form a connection point, wherein the suboccipital cordconnection node, the dorsal cord connection node, and an area of thehousing close to the dorsal cord connection node form a rear portion ofthe wearable telecommunication device, wherein the rear microphone 37 isfixed on the rear portion; and wherein a front-facing portion of theneck-wearable housing is in contact with an upper chest when worn by theuser.

When the rear microphone 37 is a part of a microphone array, the rearmicrophone signal may be used in processing a front microphone signal.In particular, the noise signal may be estimated and the estimation maybe subtracted from the front microphone signal by means of directsubtraction or spectrum-dependent subtraction as shown in FIG. 24A andFIG. 24B. Further the target signal may be processed by an active noisereduction (ANR) system which mathematically determines residual noiseestimation and subtracts it from the target signal in order toadditionally increase the SNR of the target signal.

Generally, most of optimal filters applicable for the above-indicatedtask may be considered as instances of the Wiener filter (FIG. 26A). Twosignals, x_(k) and y_(k) are simultaneously supplied to the filterinputs. The y_(k) signal usually contains two signal components, onecomponent correlating with the x_(k) signal, and another componentnon-correlating with the x_(k) signal. The Wiener filter allows optimalestimation of the y_(k) signal component correlating with the x_(k)signal, and forming an error signal by subtracting the estimation fromthe y_(k) signal.

An optimal finite impulse response (FIR) filter able to minimize aroot-mean-square error may be defined based on the autocorrelationfunction of a reference signal and the cross-correlation function of thereference signal and the processed signal. Practically, theautocorrelation and cross-correlation functions are defined based on theprevious samples of the corresponding signals, so a large amount of datais required for precisely calculating the estimation value.

Another approach for defining the filter tap weight factors is usingadaptive algorithms. Instead of forming a data set for defining thecorrelation functions and using these functions for calculating eachsingle tap weight vector for approximation of the optimal Wiener filter,the data is sequentially used for adjusting the filter tap weights inthe direction of the gradient minimizing the root-mean-square error.Generally, the filter tap weights are adjusted in response for everydata set, so this method requires substantially less adaptationcalculations for each sample, in comparison with optimal algorithms.Like an optimal filter in case of a stationary signal, an adaptivefilter automatically adjusts the filter tap weights upon driftingcorrelation functions of the input signals. An adaptive filter is ableto track statistical parameters of non-stationary signals, if theparameters change rate is slower than the convergence rate of theadaptive filter.

The most commonly used adaptation algorithm for FIR filters uses aquadratic error surface for such filters. When the filter tap weightschange by a low value, being inversely proportional to the localgradient of the filter tap weight objective function, then the tapweights tend to shift to the global minimum position of the errorsurface.

The Widrow-Hoff Algorithm has proposed tap weight adaptation method foreach sample, by using an instant gradient assumption (this methodsometimes is referred to as a stochastic gradient method), instead ofslow filter adjustment using an average gradient assumption, which mayalso be used in the invention.

The adaptive algorithm may be defined as follows:

w(n+1)=w(n)+μx(n)e(n)  (41),

where w is the adaptive filter tap weight, n is the step number, μ isthe filter convergence factor defining stability and the convergencerate of the filter. This algorithm is knows as the least-mean-square(LMS) algorithm. The LMS algorithm is simple, numerically stable and itis widely used in various adaptive systems. The diagram in FIG. 26Billustrates possible embodiment of the LMS algorithm in a filter, wherethe product of multiplication of the error signal and the referencesignal is used for adaptation of the filter tap weights.

The main advantage of the LMS algorithm is its ultimate calculationsimplicity, as just N+1 pairs of multiplication-addition actions shallbe performed in each step for adjusting the filter tap weights. Thereverse side of the simplicity is slow convergence and comparativelyhigh error dispersion in the steady state, as the filter tap weightsalways fluctuate around optimal values, thus increasing the outputnoise.

Applicability of a certain algorithm depends on numerous factors andshall be defined individually in each case, based on experimental data.For instance, when an adaptive algorithm like the LMS algorithm is used,extraction of the input signal components being correlated andnon-correlated to each other is performed in the real-time mode. It isobvious that when the above-stated microphone layout comprising a frontmicrophone and a rear microphone is used, all components in thefrequency range below 1.7 kHz will be suppressed. The non-correlationdegree of the front and rear microphone signals increases almostproportionally as the frequency rises in the range above 1.7 kHz, so theefficiency of the target signal detection increases correspondingly.

There are numerous LMS algorithm modifications aimed at increase of theconvergence rate or at decrease of the number of necessary calculations.The convergence rate increase may be attained by improvement of thegradient assumption as well as by transformation of the input signal soas to make its samples non-correlated. Decreasing the calculationcomplexity may be achieved, e.g., by using signs of the error signal andthe time-delay line content instead of their values. This approachallows getting rid of multiplication operations while updating thefilter tap weights.

Loss of the target signal in the frequency range below 1.7 kHz may becompensated by digital filtration methods. However, the SNR of harmonicvoice components will be worse in this case.

Further improvement of the noise reduction system is introducing a thirdfront microphone placed in a neck-worn device and located on the user'schest. This approach allows forming a full-size microphone array whichprovides solutions for a number of problems, e.g., dynamic forming thearray directional diagram depending on the user's head rotation andincreasing quality of the speech signal owing to widening the arrayaperture.

FIG. 27 and FIG. 28 show an embodiment of the invention in a form of awearable telecommunication device, comprising a neck-wearable housing 1configured to be mounted on a human body and in contact with back, left,right sides of the neck and upper chest and having at least oneelectronic unit 9 attached thereto, two in-ear earphones 3A, 3B, twocords 4A, 4B, one of which connects to one of the in-ear earphone to theelectronic unit, and the other cord connects the other in-ear earphoneto the electronic unit, a microphone array for picking up and processinga user's voice, comprising a front microphone 34, a rear microphone 38and processor, where the two cords are mechanically connected to theneck-wearable housing and points of connection of the two cords to theneck-wearable housing are close to each other and form a dorsal cordconnection node 5, and are further mechanically connected to each otherin sections between the in-ear earphones and the dorsal cord connectionnode to form a suboccipital cord connection node 6 at the connectionpoint, where the rear microphone 34 is on a portion of the neck-wearablehousing configured to be in contact with a back of the neck when worn bythe user; and where a correlated portion of the signal from the rearmicrophone and the signal from the front microphones represents noise,while an uncorrelated portion of the signal represents useful data.

The rear microphone may be fixed on the suboccipital cord connectionnode (37 on FIGS. 28, 29A), on the neck-wearable housing close to thedorsal cord connection node (38 on FIG. 29A), and between thesuboccipital cord connection node and the dorsal cord connection node.The front microphone 25 is fixed on a portion of the neck-wearablehousing that is in contact with the user's chest when worn by the user(FIG. 15).

In some embodiments (FIG. 29B) the wearable device comprises two frontmicrophones 36A, 36B wherein the two front microphones are fixed on aportion of the neck-wearable housing that is in contact with the user'schest and at a substantially the same height when worn by the user. Inparticular, the front microphone 36B is positioned on the left side ofthe user's chest, the front microphone 36A is positioned on the rightside of the user's chest. The rear microphone 38 is positioned in closeproximity to the dorsal node (FIGS. 28, 29A, 29B).

This configuration allows implementation of an adaptive algorithmdefining the correlated and non-correlated components of the signalseparately for two pairs of microphones, front right—rear and frontleft—rear, which facilitates substantially increasing precision of thenoise signal assumption and improving SNR of the target speech signal.

The device may further include a phased or a gradient microphone arraycomprising at least two microphones fixed on a chest portion of theneck-wearable housing, the additional microphone array may be used todetermine a directional diagram of received sound waves.

Additionally, the target speech signal SNR may be improved byintroducing one more microphone disposed below the pair of thefront-right and front-left microphones so as to form a triangle (likeshown in FIG. 22B), or by introducing two more microphones 34, 35disposed below the pair of front-right and front-left microphones so asto form a tetragon (like shown in FIG. 29B). This configuration providesfurther improvement of the signal-to-noise ratio owing to an increase inthe number of microphones in the array and possibly using morecomplicated adaptation algorithms, e.g., a phased sub-array or agradient sub-array may be formed so as to determine the direction of thetarget sound and the direction of the noise sound.

FIG. 29A and FIG. 29B show an embodiment of the invention in a form of awearable electronic device comprising a neck-wearable housing 1 with atleast one electronic unit 9 attached thereto, two in-ear earphones 3A,3B, two cords 4, and a microphone array comprising four frontmicrophones 34, 35, 36A, 36B and two rear microphones 37, 38, where thefront microphones 36A, 36B are positioned on a substantially horizontalline (the first line), the front microphones 34, 35 are positioned onanother substantially horizontal line below the first line. Theneck-wearable housing is configured so as the front microphones 34, 35are disposed in close vicinity of the left and right clavicles,correspondingly.

The dorsal node 5 and the suboccipital node 6 comprise the two rearmicrophones 38, 37, correspondingly. The microphone array forms a numberof signals further used for determination of the correlated andnon-correlated components of the front and rear microphone signals,while the correlated components are considered as noise. The adaptivealgorithms used for determination of the correlated and non-correlatedcomponents may be narrow-band algorithms or wide-band algorithms. Thenarrow-band adaptive algorithms are far simpler in implementation thanthe wide-band adaptive algorithms. Whether an algorithm shall beimplemented as narrow-band or wide-band is determined based on the phaseincursion between the microphones in a certain frequency range, see [8]:

$\begin{matrix}{{{\Delta\phi} = {2\pi \frac{\Delta \; {{Fs} \cdot L}}{c}{\operatorname{<<}1}}},} & (42)\end{matrix}$

where ΔFs is the frequency range, L is the distance between theoutermost microphones, c is the velocity of sound in the atmosphere(approximately 340 meters per second).

In the device under consideration, ΔFs=Fmax−Fmin=3.1 kHz, where Fmax=3.4kHz is the highest signal frequency, Fmin=300 Hz is the lowest signalfrequency, L=0,2 M is the distance between the outermost microphones, sothe phase incursion Δφ≈11.5 and the condition (42) is not met.Therefore, wide-band adaptive algorithms shall be used in the deviceunder consideration.

When the noise signal is adaptively suppressed, the target signal issomewhat attenuated as well, because the noise signal mainly differsfrom the target signal by the direction of incoming sound wave. If thedirection of the target sound is known, then an adaptive Frost algorithmmay be used, see [6], which limits attenuation of the target signal.When a front microphone is positioned on the user's head (like a boommicrophone), the adaptive Frost algorithm may be used fairly easily.However, when one or more front microphones are placed in the device andpositioned on the user's chest, the direction of incoming target soundmay be determined very roughly within a rather wide angle range due topossible rotation of the user's head. Nevertheless, the adaptive Frostalgorithm may be used if one of the front microphones is selected as thebest one, based on the target signal volume.

Another approach is using a processed composite signal formed fromseveral front microphones as the front signal in the adaptive Frostalgorithm. One other approach is using one or more front microphonesdisposed in additional devices like glasses, watches, bracelets, rings,etc., where the front microphones are wirelessly connected to thewearable device.

FIG. 30 shows an embodiment of the invention, where two frontmicrophones 42, 43 are located in the glasses frame 44 of an additionalaccessory, glasses 45. The microphones placed in the glasses aredirected towards the user's mouth.

Still another approach to adaptive filter improvement is detectingsilence periods in the user's speech and calculating the filter tapweights during these gaps. However, this algorithm requires a silencesensor to detect the speech gaps. An accelerometer may be used as thesilence sensor, when the accelerometer is located in a portion of thedevice that is adjacent to the user's body surface, e.g., in the area ofthe temporomandibular joint. Alternatively, the earphones may comprisethe silence sensor adjacent to the user's external auditory canal. Yetthis method has some limitations diminishing its advantages. First, anynon-intentional movement of the sensor relative to the user's body (likehiccups, yawning, chewing, etc.) results in rustles that are detected asthe user's speech, and loose engagement of the sensor (e.g., due tobristle, skin roughness, skin and intra-ear secretions, etc.) causesconsiderable malfunction of such noise reduction systems.

Using at least two microphones, where some of them are front microphonesand some are rear microphones, allows detecting the speech gaps byanalyzing the signal level. When the signal level in all microphones ofthe array is similar (i.e., the signals are correlated), then a speechgap is detected and the filter tap weights may be adjusted, and when thesignal level of the front microphone is substantially greater than thesignal level of the rear microphone, then the target signal is detectedand processed.

Calculation of the filter tap weights may be performed during the speechgaps, based on a projection algorithm, see [7] having high efficiency,fast convergence and relatively low calculation complexity. Further theprojection algorithm is briefly discussed.

Each microphone signal spectrum can be determined based on the FastFourier Transform (FFT):

$\begin{matrix}{{{{Sp}\left( {{mf},{mi},k} \right)} = {\sum\limits_{{nt} = 0}^{{NFTT} - 1}{{S\left( {{{\left( {{nt} + {{NFTT} \cdot k}} \right) \cdot \Delta}\; T},{mi}} \right)}^{{- }\frac{2\pi}{NFFT}{{nt} \cdot {mi}}}}}},} & (43) \\{\mspace{79mu} {{{mf} \in \left\lbrack {0,{{NFFT}/2}} \right\rbrack},\mspace{79mu} {{mi} \in \left\lbrack {0,{{Mic} - 1}} \right\rbrack},\mspace{79mu} {k \in 0},1,2,\ldots \mspace{14mu},}} & (44)\end{matrix}$

where Sp (mf, mi, k) is the signal spectrum value for the sample numbermf for the microphone number mi and for the processing cycle number k; S((nt+NFTT×k)×ΔT, mi) is the signal value for the time count number(nt+NFTT×k) and for the microphone number mi; ΔT=(Fd)⁻¹ is the samplingperiod in the analog-to-digital converter (ADC); Fd>2×Fmax is thesampling frequency in the ADC (Fmax is the highest target signalfrequency); NFFT is the number of time counts while the signal spectrumis formed; Mic is the number of microphones in the device.

Further the signal correlation matrix is formed for NumD frequencyranges:

K(mi,mi1,nd,k)=Σ_(kf=0) ^(MaxFD-1)[Sp(kf+nd·MaxFD,mi,k)·Sp(mf+nf·MaxFD,mi1,k)*],ndε[0,numD−1],  (45),

where MaxFD is the number of spectral samples in a frequency sub-range;NumD=round (NFFT×(Fmax−Fmin)/(Fd×MaxFD)) is the number of frequencysub-ranges in the operational bandwidth.

The MaxFD value is determined so as to meet the following twoconditions: the narrow-band condition

2πMaxFd×Fd×L/(NFFT×c)<<1  (46),

and the stable estimation of the correlation matrix condition

MaxFD>2×Mic  (47).

A weight factor is formed for every frequency sub-range so as tosuppress the interfering noise signals:

{right arrow over (C)}(nd)=(I−K _(I)(nd)·(K _(I)(nd)·K _(I)(nd))⁻¹ ·K_(I)(nd)·{right arrow over (S)}(nd)  (48),

where I is a unitary matrix having dimension Mic; K_(I)(nd) is thematrix composed of I columns of the correlation matrix (45); {rightarrow over (S)}(nd) is the reference vector having dimension Mic andproviding directing the microphones to the user's mouth in the frequencysub-range nd.

The vector element for the microphone number mi is:

$\begin{matrix}{{{S\left( {{nd},{mi}} \right)} = {K_{mi}^{{- }{\frac{2{\pi \cdot R_{mi}}}{c} \cdot {({{Fmin} + {\frac{{Fd} \cdot {MaxFD}}{NFFT}{nd}}})}}}}},} & (49)\end{matrix}$

where Rmi is the distance between the user's mouth and the microphonenumber mi; Kmi is sensitivity of that microphone depending on themicrophone position.

The above relatively simple expression is generally not valid whendiffraction occurs, as the wave front is substantially corrupted.Therefore, the above model is satisfactorily describes the signalsobtained from microphones located in the area of ideal, non-distortedwave front as defined in the expression (40). However, according toexperimental data, the expression (49) still may be used for lowfrequency signals even in diffracted area, as the sound phase is almostlinearly depends on frequency (FIG. 23B).

The resulted signal spectrum is formed as follows:

$\begin{matrix}{{{{Sp}\; 0\left( {{{kf} + {{Max}\; {{FD} \cdot {nd}}}},k} \right)} = {\sum\limits_{{mi} = 0}^{{Mic} - 1}{{C^{*}({mi})} \cdot {{Sp}\left( {{{kf} + {{Max}\; {{FD} \cdot {nd}}}},{mi},k} \right)}}}},\mspace{79mu} {{kf} \in \left\lbrack {0,{{Max}\; {FD}}} \right\rbrack},\mspace{79mu} {{nd} \in \left\lbrack {0,{{NumD} - 1}} \right\rbrack},} & (50)\end{matrix}$

The resulted time-domain signal is formed, based on the Inverse FourierTransform (IFT):

$\begin{matrix}{{{S\; 0\left( {{nt},k} \right)} = {\sum\limits_{{mf} = 0}^{{NFFT}/2}{{{Sp}\left( {{mf},k} \right)}^{\frac{2\pi}{NFFT}{{nt} \cdot {mf}}}}}},{{nt} \in \left\lbrack {0,{{NFFT} - 1}} \right\rbrack},{k \in 0},1,2,{\ldots \mspace{14mu}.}} & (51)\end{matrix}$

When the process is divided into two stages as described in the above,the subtraction of the noise signal may advantageously be provided onthe first stage, when the user speaks, whereas selection of the weightfactors and direction vectors (see the expression (49)) may be performedon the second stage during the speech gaps, which allows substantialimproving the noise reduction efficiency.

Obviously, if a microphone of the microphone array shall be positionedas a rear microphone, it is expedient to place it in a neck-worn device.The neck-worn device may be implemented as a wireless headset, awearable electronic device, a wearable multimedia device, a wearablepersonal computer, a hearing aid, etc. provided in a form of a necklaceor otherwise comprising a neck-wearable housing, wherein the frontmicrophones are positioned on the user's chest, while the rearmicrophone or microphones may be positioned on the back surface of ahelmet, a headwear piece, a shirt collar, or in a rear cord connectionnode of the device, which is preferable embodiment of the invention.

The neck-worn device may comprise a neck-wearable housing in any form.The neck-worn device may be based on an O-shaped loop as shown in FIG.29B, or it may be based on a U-shaped loop (FIG. 15) comprising the samefront microphones.

In this discussion, neck-wearable housing of the claimed device ismainly described as O-shaped or U-shaped loop in examples andembodiments. However, other types of neck-wearable housing may bepossible.

In many embodiments the neck-wearable housing may be flexible in atleast one location, for example the portions of a neck-wearable housingbetween dorsal node 5 and electronic unit 9 are flexible (FIGS. 15, 28).Also, the entire housing may be flexible as well.

As the position of the rear microphone is predetermined and fixed inrelation to the front microphones of the wearable device, and thedistance between the rear microphone and the target sound source isknown as well (at least roughly), then diffraction effects occurringwhile sound waves pass around a human head may be considered asaccountable factors, see [11].

However, positioning the rear microphone under clothes causessubstantial distortion of the sound received by this microphone. This iswhy positioning the rear microphone in a rear cord connection node isideal in view of providing the best possible noise reduction processingof the target signal. For example, when the rear microphone 37 is placedin the suboccipital node 6 (FIG. 25), its position is fixed in relationto the front microphones, no matter if the user's head is rotated ornot, as the earphone cords adhere to the user's head by tension forceand the suboccipital node moves along with the corresponding point ofthe back surface of the user's neck. Moreover, in this case, the rearmicrophone is not covered by clothes even if the neck loop itself islocated under the clothes.

Alternatively, the rear microphone 38 may be placed in the dorsal node 5(FIG. 29A). This option may be advantageous when the user has long hairor uses a headwear article (typically like female users) which may coverthe suboccipitally positioned microphone and impede penetration ofacoustic waves. Moreover, this option may be still advantageous evenwhen the user has short hair or a bald head, as the rear microphoneplaced in the dorsal node is better protected against wind by theclothes.

In one embodiment of the invention, the rear microphone 38 may bemovably positioned between the suboccipital 6 and dorsal 5 nodes (FIG.31), so the user is able to choose and use the best rear microphoneposition, depending on the operation conditions (the type of usedclothes, wind, rain, acoustic environment, etc.). This option requires aseparate cord for the rear microphone (like the helical cord 46 in FIG.31), but such a feature may hardly be considered as a substantialdrawback in view of the obvious advantages thereof.

In another embodiment of the invention, the rear microphone may beselected among the two rear microphones, where one of them is located inthe suboccipital node and another one is located in the dorsal node,depending on the device operation conditions. For instance, when theuser walks in the street, the suboccipital node position may bepreferable for the rear microphone, and when the user drives a car, thedorsal node position may be preferable due to proximity of the headrestraint. Sometimes, the earphones may be retracted, so the dorsal nodeposition and the suboccipital node position may be positioned fairlyclose to each other. This option is illustrated by FIG. 32 and FIG. 33.The selection may be done manually by the user (e.g., via the deviceuser interface) or automatically, based on the analysis and comparisonof quality of signals of the rear microphones.

In still another embodiment of the invention, the rear microphone signalmay be composed of the signals obtained from two rear microphones, e.g.,using one or more of the processing algorithms described in the above.

Thus, owing to the necklace-like form-factor of the wearable device andthe presence of the suboccipital and dorsal cord connection nodes, thefront microphones may be positioned in the area of direct propagation ofthe speech sound wave, while the rear microphone (or several rearmicrophones) used as the noise sound wave receiver(s) may be positionedon the back surface of the user's neck in the area of the acousticshadow for the speech sound wave. This layout pattern allows forming acorrelation microphone array, wherein components of the front signalcorrelated with the rear signal may be treated as noise, whilecomponents of the front signal non-correlated with the rear signal maybe treated as the target signal.

The first step of the signal processing includes forming a compositefront signal comprising an additive mix of a noise signal and a targetsignal, obtained from the front microphone(s). The rear microphone(s)form(s) a rear signal comprising mainly a noise signal. Further, bothsignals are processed by an adaptive digital filter (e.g., a Wiener-likefilter) so as to extract the target signal, using the LMS method. Thesystem may be described by the following equations:

e _(n) =d _(n) −y _(n)  (52),

y _(n) =w _(n) ^(T) x _(n)  (53)

where e_(n) is the filtered target signal; d_(n) is the combined frontsignal; y_(n) is the filtered noise signal; w_(n) ^(T) is a transposedmatrix of adaptive filter tap weights w_(n); x_(n) is the combined rearsignal.

The adaptation principle is described as follows:

w _(n+1) =w _(n) +μe _(n) x _(n)  (54),

where n is the adaptation step number; μ is a positive constant definingstability and the convergence rate of the algorithm.

The correlation between the input signal x_(n) and the output signald_(n), may be presented as a discrete transfer function. Aftersuccessful adaptation, W(z) acceptably approximates the transferfunction, so the adaptive filter may identify the system transferfunction.

In the Filtered-x LMS algorithm (e.g., see [12]), P(z) is the systemtransfer function, {circumflex over (P)}(z) is the system transferfunction model obtained by the identification. In this case the systemis described as follows:

e _(n) =d _(n) −P(z)y _(n)  (55),

where y_(n) is the same as in the expression (53), but the expression(54) is modified in the following way:

w _(n+1) =w _(n) +μe _(n) r _(n)  (56),

where r _(n) is a vector formed from current and previous samples of thefiltered reference signal r_(n)

r _(n) ={circumflex over (P)}(z)x _(n)  (57).

The function {circumflex over (P)}(z) may be presented either by afinite-impulse response (FIR) filter or an infinite-impulse response(IIR) filter; however, FIR filters are used more commonly owing to theirhigher stability. Identification of the function P(z) may be performedby a usual LMS algorithm. When the identifying signal is a white noise,then W(z) acceptably accurate approximates P(z). The system isconsidered stable if the phase error of the model does not exceed π/2.Thus, the output signal may be formed as defined in the expression (52).

In real operating conditions, the disturbance and the system responsecannot be measured with ideal accuracy, so iterative methods can be usedin order to maintain the algorithm convergence. This approach may beadvantageous when processing non-stationary signals, though the signalduration shall exceed the disturbance duration.

Having thus described a preferred embodiment, it should be apparent tothose skilled in the art that certain advantages of the described methodand apparatus have been achieved.

It should also be appreciated that various modifications, adaptations,and alternative embodiments thereof may be made within the scope andspirit of the present invention. The invention is further defined by thefollowing claims.

LIST OF CITED REFERENCES

-   1. J. Benesty, J. Chen, Y. Huang, I. Cohen, “Noise reduction in    speech processing”, Springer Science & Business Media (Apr. 28,    2009).-   2. O. Hirsch, “Bluetooth microphone array”, US 2010/0048131 A1    (2010).-   3. G. C. Burnett, “Microphone array with rear venting”, US    2009/0003640 A1 (2009).-   4. A. L. Ushakov, “Headset for a mobile electronics”, US    2014/0185821 A1 (2014).-   5. Hyun Jun Park, Kwokleung Chan, “Systems, methods, apparatus and    computer program products for enhanced active noise cancellation” US    2010/0131269 A1 (2010)-   6. J. Benesty, J. Chen, Y. Huang “Microphone Array Signal    Processing”, Springer Topics in Signal Processing (2008).-   7. Malyshkin, G. S., Optimal and adaptive methods of processing of    hydroacoustic signals, v. 1, v. 2, St. Petersburg, “Electropribor”    publishing, 2009.-   8. Monsingo, R. A., Miller, T. U. Adaptive antenna arrays.    Introduction to Theory, Radio and Communications, 1986, p. 448.-   9. Sementsov et al., Research into acoustic transfer functions and    speech clarity for wearable devices, www.necktec.ru, downloaded 22    Nov. 2015-   10. Irina Aldoshina, Bi-aural Current status of research,    http://www.show-master.ru/ Downloaded 22 Nov. 2015-   11. Mayer, R. Numerical methods of solving of edge cases or a    vibrating membrane, http://mathhelpplanet.com/ Downloaded 22 Nov.    2015-   12. Asutosh Kar, A bika Prasad Chanda Sarthak Mohapatra Mahesh    Chandra An Improved Filtered-x Least-mean-square Algorithm for    Acoustic Noise Suppression.//Advanced Computing and Informatics.    Proceedings of the Second International Conference on Advanced    Computing, Networking and Informatics (ICACNI-2014), vol. 1 pages    25-32, Springer International Publishing (2014).

What claimed is:
 1. A headset for a mobile electronic device,comprising: a neck-wearable housing having a generally U-shape with anelectrical connector attached thereto; two in-ear earphones; two cords,each connected at one end to a corresponding in-ear earphone andconnected at its other end to the electrical connector; wherein the twocords are mechanically connected to the neck-wearable housing, andpoints of connection of the cords to the neck-wearable housing are inclose proximity to each other and form a dorsal cord connection node,and wherein the two cords are also mechanically connected to each otherin sections between the in-ear earphones and the dorsal cord connectionnode to form a suboccipital cord connection node at the connectionpoint.
 2. The headset of claim 1, wherein the dorsal cord connectionnode and the suboccipital cord connection node are located on a dorsalsurface of a neck, and cords in sections between the in-ear earphonesand the suboccipital node are located over an auricle.
 3. The headset ofclaim 1, wherein the suboccipital cord connection node is a clip adaptedto move along the two cords for adjusting a length of the two cords. 4.The headset of claim 1, wherein the suboccipital node comprises anelectrical connector for disconnecting the cords.
 5. The headset ofclaim 1, wherein at least one of the two cords is a helical spring in asection between the suboccipital and dorsal cord connection nodes. 6.The headset of claim 1, further comprising an electronic unitmechanically and electrically coupled to the electrical connector. 7.The headset of claim 6, further comprising buttons disposed on theneck-wearable housing for control of the electronic unit.
 8. The headsetof claim 6, further comprising at least one power supply for theelectronic unit, the power supply disposed on the neck-wearable housing.9. The headset of claim 1, further comprising at least one noisereduction microphone array disposed on the mobile electronic device. 10.The headset of claim 1, wherein the neck-wearable housing is flexible inat least one location.
 11. A wearable telecommunication device,comprising: a neck-wearable housing with an electronic unit attachedthereto; two in-ear earphones; two cords, one of which connects to oneof the in-ear earphone to the electronic unit, and the other cordconnects the other in-ear earphone to the electronic unit; and amicrophone array for picking up and processing a user's voice, themicrophone array comprising a front microphone, a rear microphone and aprocessor; wherein the two cords are mechanically connected to theneck-wearable housing, and points of connection of the two cords to theneck-wearable housing are close to each other and form a dorsal cordconnection node, and are further mechanically connected to each other insections between the in-ear earphones and the dorsal cord connectionnode to form a connection point; wherein the suboccipital cordconnection node, the dorsal cord connection node, and an area of thehousing close to the dorsal cord connection node form a rear portion ofthe wearable telecommunication device; wherein the rear microphone isfixed on the rear portion; and wherein a front-facing portion of theneck-wearable housing is in contact with an upper chest when worn by theuser.
 12. The device of claim 11, wherein the rear microphone is fixedon the suboccipital cord connection node.
 13. The device of claim 11,wherein the rear microphone is fixed on the neck-wearable housing closeto the dorsal cord connection node.
 14. The device of claim 11, whereinthe rear microphone is between the suboccipital cord connection node andthe dorsal cord connection node.
 15. The device of claim 11, furthercomprising a spring between the suboccipital cord connection node andthe dorsal cord connection node.
 16. The device of claim 15, wherein therear microphone is fixed on the spring.
 17. The device of claim 11,wherein the rear microphone detects surrounding noise, and wherein acorrelated portion of the signal from the rear microphone and the signalfrom the front microphone represents noise, while an uncorrelatedportion of the signal represents a useful data.
 18. The device of claim17, wherein signals from the rear microphone and the front microphoneare ignored when their correlation is above a pre-defined threshold. 19.The device of claim 11, wherein the front microphone is fixed on thefront-facing portion of the neck-wearable housing
 20. The device ofclaim 11, wherein the microphone array includes at least two frontmicrophones, wherein the two front microphones are fixed on thefront-facing portion of neck-wearable housing at a substantially thesame height when worn by the user and one of the at least two frontmicrophones is close to or below a right clavicle of the user, and theother of the at least two front microphones is close to or below a leftclavicle of the user.
 21. The device of claim 11, further comprising atleast one gradient microphone array comprising at least two frontmicrophones fixed on the front-facing portion of the neck-wearablehousing at different heights when worn by the user, wherein the gradientmicrophone array is used to determine a directional diagram of receivedsound waves.
 22. The device of claim 11, further comprising at least onephased microphone array comprising at least two front microphones fixedon the front-facing portion of the neck-wearable housing at differentheights when worn by the user, wherein the phased microphone array isused to determine a directional diagram of received sound waves.
 23. Thedevice of claim 11 further comprising an electronic accessory in a formof a wrist watch, which is wirelessly connected to the electronic unit,wherein the electronic accessory includes the front microphone.
 24. Thedevice of claim 11, further comprising an electronic accessory in a formof a finger ring, which is wirelessly connected to the electronic unit,wherein the electronic accessory includes the front microphone.
 25. Thedevice of claim 11 further comprising an electronic accessory in a formof eyeglasses, which is connected to the electronic unit, wherein theelectronic accessory includes the front microphone.
 26. The device ofclaim 11, wherein neck-wearable housing is generally U-shaped.
 27. Thedevice of claim 11, wherein the neck-wearable housing is generallyO-shaped.
 28. The headset of claim 11, wherein the neck-wearable housingis flexible in at least one location.
 29. A wearable telecommunicationdevice, comprising: a neck-wearable housing configured to be mounted ona human body and in contact with back, left, right sides of the neck andupper chest and having at least one electronic unit attached thereto;two in-ear earphones, two cords, one of which connects to one of thein-ear earphone to the electronic unit, and the other cord connects theother in-ear earphone to the electronic unit, a microphone array forpicking up and processing a user's voice, comprising a front microphone,a rear microphone and processor; wherein the two cords are mechanicallyconnected to the neck-wearable housing and points of connection of thetwo cords to the neck-wearable housing are close to each other and forma dorsal cord connection node, and are further mechanically connected toeach other in sections between the in-ear earphones and the dorsal cordconnection node to form a suboccipital cord connection node at theconnection point; wherein the rear microphone is on a portion of theneck-wearable housing configured to be in contact with a back of theneck when worn by the user; and wherein a correlated portion of thesignal from the rear microphone and the signal from the frontmicrophones represents noise, while an uncorrelated portion of thesignal represents useful data.
 30. The device of claim 29, wherein therear microphone is fixed on any of (i) the suboccipital cord connectionnode, (ii) the neck-wearable housing close to the dorsal cord connectionnode, and (iii) between the suboccipital cord connection node and thedorsal cord connection node.
 31. The device of claim 29, furthercomprising a spring between the suboccipital cord connection node andthe dorsal cord connection node, wherein the rear microphone is on thespring.
 32. The device of claim 29, wherein the front microphone isfixed on a portion of the neck-wearable housing that is in contact withthe user's chest when worn by the user.
 33. The device of claim 29,wherein signals from the rear microphone and the front microphone areignored when their correlation is above a pre-defined threshold.
 34. Thedevice of claim 29, wherein the device forms an output signal e_(n) as:e _(n) −d _(n) −y _(n), where y_(n) is a correlated signal representingfiltered noise calculated as:y _(n) =w _(n) ^(T) x _(n), where x_(n) is a combined signal from therear microphone, d_(n) is a combined signal from the front microphones,w_(n) are adaptive filter coefficients defined as:w _(n+1) =w _(n) +μe _(n) x _(n), where w_(n+1) is a set of coefficientsat a current moment of time n+1, w_(n) is a set of coefficients at aprevious moment of time, n is defined by a clock rate of the incomingdata stream, is a positive value defining stability and convergencerate.
 35. The device of claim 29, wherein the device forms an outputsignal e_(n) based on a Filtered-X Least-Mean-Square (FXLMS) algorithm:e _(n) −d _(n) −P(z)y _(n), where d_(n) is a combined signal from thefront microphones, P(z) is a transfer function, and y_(n) is acorrelation signal defined by:y _(n) =w _(n) ^(T) x _(n), where x_(n) is a combined signal from therear microphone, w_(n) are adaptive filter coefficients defined as:w _(n+1) =w _(n) +μe _(n) r _(n), where w_(n+1) is a set of coefficientsat a current moment of time n+1, w_(n) is a set of coefficients at aprevious moment of time n, n is defined by a clock rate of the incomingdata stream, μ is a positive value defining stability and convergencerate, r _(n) is a vector formed by current and previous values of afiltered base signal r_(n) according to:r _(n) ={circumflex over (P)}(z)x _(n), where {circumflex over (P)}(z)is based on a Least Mean Squares Algorithm that corresponds to a finiteimpulse response (FIR) filter.
 36. The device of claim 29, wherein themicrophone array includes two front microphones, wherein the two frontmicrophones are fixed on a portion of the neck-wearable housing that isin contact with the user's chest and at a substantially the same heightwhen worn by the user and one of the two front microphones is close toor below a right clavicle of the user, and the other of the two frontmicrophones is close to or below a left clavicle of the user.
 37. Thedevice of claim 29, further comprising at least one gradient microphonearray comprising at least two front microphones fixed on thefront-facing portion of the neck-wearable housing at different heightswhen worn by the user, wherein the gradient microphone array is used todetermine a directional diagram of received sound waves.
 38. The deviceof claim 29, further comprising at least one phased microphone arraycomprising at least two front microphones fixed on the front-facingportion of the neck-wearable housing at different heights when worn bythe user, wherein the phased microphone array is used to determine adirectional diagram of received sound waves.
 39. The device of claim 29,wherein the rear microphone is used as a detector of surrounding noisewherein a correlated portion of the signal from the rear microphone andthe signal from the front microphone represents noise, while anuncorrelated portion of the signal represents a useful data.
 40. Thedevice of claim 29, wherein signals from the rear microphone and thefront microphone are not transmitted when their correlation is above apre-defined threshold.
 41. The device of claim 29, wherein neck-wearablehousing generally is U-shaped.
 42. The device of claim 29, wherein theneck-wearable housing generally is O-shaped.
 43. The headset of claim29, wherein the neck-wearable housing is flexible in at least onelocation.
 44. A wearable telecommunication device, comprising: aflexible neck-worn sheath with at least one electronic unit attachedthereto; two in-ear earphones; two cords, one of which connects to oneof the in-ear earphone to the electronic unit, and the other cordconnects the other in-ear earphone to the electronic unit, wherein thetwo cords are mechanically connected to the neck-worn sheath, and pointsof connection of the two cords to the neck-worn sheath are close to eachother and form a dorsal cord connection node, and are furthermechanically connected to each other in sections between the in-earearphones and the dorsal cord connection node to form a suboccipitalcord connection node at the connection point; and a rear microphone inthe suboccipital cord connection node or in the dorsal cord connectionnode.